太空發射系統

美国运载火箭
(重定向自空间发射系统

太空發射系統(英語:Space Launch System,簡稱「SLS」)是NASA自2011年以来开发的一种基於太空梭技術的重型運載火箭。SLS火箭目前的主要用途是搭載獵戶座太空船進行阿提米絲計畫,火箭将从位于佛罗里达州肯尼迪航天中心LC-39B发射台發射升空。在前四次阿耳忒弥斯任务之后,美国宇航局计划将太空发射系统的生产和发射移交给深空运输公司(Deep Space Transport LLC),这是波音和诺斯洛普·格鲁门的合资企业[17]。不過,预计至少在2030年之前,阿耳忒弥斯计划每年最多使用一次SLS[18]

太空發射系統
搭载獵戶座飛船的太空發射系統Block 1
用途重型運載火箭
制造国家 美国
项目成本238亿美元(名义上)[1]
单次发射费用超过20亿美元,不包括开发费用(估计值)[2][1]
外型及质量参数
高度320英尺(98米)(載人版本)
400英尺(120米)(貨艙版本)
直径核心段27.6英尺(8.4米)
质量2,497,000公斤(5,505,000英磅)(載人版本)
2,951,000公斤(6,506,000英磅)(貨艙版本)
级数2
酬載量
LEO [註 1]有效载荷
质量
  • Block 1: 95 t(209,000磅)[4]
  • Block 1B: 105 t(231,000磅)[5][6]
  • Block 2: 130 t(290,000磅)[7]
地月轉移有效载荷
质量
  • Block 1: > 59,500磅(27 t)[8][9]
  • Block 1B Crew: 83,700磅(38 t)
  • Block 1B Cargo: 92,500磅(42 t)
  • Block 2 Crew: > 94,700磅(43 t)
  • Block 2 Cargo: > 101,400磅(46 t)
相关火箭
相似型号
发射历史
现状服役
发射场甘迺迪太空中心39B号发射台
总发射次数1
成功次数1
著名载荷猎户座飞船
助推器 (Block 1, 1B)
助推器數2台五段式固體火箭助推器
高度54米(177英尺)[10]
直径3.7米(12英尺)
总重730 t(1,600,000磅)[10]
发动机固體燃料
单发推力海平面:3,280,000 lbf(14.6 MN;1,490 tf
真空:3,600,000 lbf(16 MN;1,600 tf[11]
总推力海平面:6,560,000 lbf(29.2 MN;2,980 tf
真空:7,200,000 lbf(32 MN;3,300 tf
比冲269 s(2.64 km/s
推进时间126 秒
燃料PBANAPCP
芯一级 (Block 1, 1B, 2) – 核心级
高度212英尺(65米)[12]
直径27.6英尺(8.4米)
空重187,990磅(85 t)
总重2,365,000磅(1,073 t)
发动机4台RS-25D/E发动机
单发推力海平面:418,000 lbf(1.86 MN)[13]
真空:512,300 lbf(2.279 MN)[13]
比冲海平面:366 s(3.59 km/s)[13]
真空:452 s(4.43 km/s)[13]
推进时间480 秒
燃料液態氫/液態氧
芯二级 (Block 1) – 临时低温推进上级英语Delta Cryogenic Second Stage
高度13.7米(45英尺)[14]
直径5米(16英尺)
空重3,490公斤(7,690磅)[15]
总重32,066公斤(70,693磅)
发动机1台RL10B-2/C-2发动机
单发推力110.1 kN(24,800 lbf
比冲465.5 s(4.565 km/s)[16]
推进时间1125 秒
燃料液態氫/液態氧
芯二级 (Block 1B, Block 2) – 探索上面级英语Exploration Upper Stage
高度17.3米(57英尺)[15]
直径8.4米(28英尺)
发动机4台RL10C-3发动机、4台RL10C-X发动机
单发推力407.2 kN(91,500 lbf
推进时间
  • 350 秒 (LEO ascent)
  • 925 秒 (TLI burn)
燃料液態氫/液態氧

SLS旨在成為退役太空梭的繼任者以及NASA深空探索計劃的主運載火箭[19][20][21]。SLS因利用了貨架上的現有的成熟技術,故取代了新開發戰神一號戰神五號運載火箭的昂貴計畫,當時这些运载火箭与「星座计划」的其他部分一起被歐巴馬政府取消,而「星座计划」曾是美国旨在重返月球的计划[22][23][24]。载人月球飞行计划,改編入阿耳忒弥斯计划的一部分,也为可能的载人火星任务作准备[25][26]。SLS正在分三个主要阶段开发:Block 1、Block 1B和Block 2,其业载量不断增加[4]。截至2019年8月 (2019-08),SLS Block 1运载火箭将发射前三次阿提米絲任務[27],随后的五次SLS飞行计划使用Block 1B,之后的所有飞行将使用Block 2[28][26][29]

美国国会在2016年12月授權进行首次發射[30],但SLS的发射至少被推遲了16次,最終2022年才首飛,比原来的6年计划增加了5年多。[註 2][31]

設計

太空發射系統是一種太空梭衍生運載火箭英语Shuttle-derived vehicle。起飞阶段由一個核心級和兩個改進的航天飞机固体助推器提供動力,上面级负责将有效载荷送入特定的轨道。所有的太空發射系統型號使用同一種核心級,它們之間的差別在於助推器和上面級。[32][33][34][35]

核心級

 
太空发射系统的三种不同型号:Block 1、Block 1B、Block 2
 
SLS核心阶段从Michoud 装配设施推出,准备运送到斯坦尼斯航天中心

核心級和助推器負責將上面級和有效載荷送出大氣層並加速到接近軌道速度。核心級包括4台RS-25引擎、液氫燃料箱和液氧氧化劑箱、固體助推器連接點、航空電子設備和主推進系統(MPS)。主推進系統為四台RS-25引擎供应燃料和氧化劑[32],并使用液壓驅動引擎的萬向節,以及對推進劑罐加壓。核心級的四台RS-25引擎在起飛時提供了大約25%的推力。[36][37] 核心級長65米,直徑8.4米,在結構和外觀上類似于航天飞机外储箱[23][38] 核心級的前四次發射使用16台太空梭任務剩下的RS-25D引擎。[39][40][41] 洛克达因公司對這些引擎進行了現代化改造以適應太空發射系統。[42] 之後的發射將使用優化的RS-25E引擎,每臺的成本降低30%以上,推力較RS-25D的2,281千牛增加到了2,321千牛。[43][44][45][46]

助推器

太空發射系統Blocks 1和Blocks 1B型使用兩個五段式固体火箭助推器,这些助推器基于四段式航天飞机固体助推器额外添加一段而成,除此之外还使用了新的航空电子设备和更轻的绝缘材料,并去掉了降落伞回收系统。[47] 五段式固体火箭助推器比四段式航天飞机固体助推器多提供了25%的冲量,但在使用后不能回收。[48][49]

太空發射系統Blocks 1和Blocks 1B型使用的五段式固体火箭助推器由于库存限制只能支持八次发射。[50] 于是在2019年3月2日提出了助推器报废和延长寿命计划(BOLE)。该计划是由诺斯洛普·格鲁门开发制造新型的固体火箭助推器,用以支持之后的Blocks 2型太空發射系統。这些助推器源自已经取消的OmegA运载火箭的复合外壳固体火箭助推器,助推器性能的提升可使Blocks 2型的近地轨道有效载荷增加到130 t(130 long ton;140 short ton)地月转移轨道有效载荷增加到46 t(45 long ton;51 short ton)。[51][52][53] 截至2021年7月 (2021-07), BOLE正在大力发展, 预计将于2024年首次点火测试。[51]

上面级

临时低温推进上级(ICPS)将在太空發射系統Block 1型的前三次阿耳忒弥斯登月计划发射中使用。[54] ICPS源自拉长的德尔塔-4运载火箭上面级,由一台RL10火箭发动机提供动力。用于发射的第一个ICPS将使用RL10 B-2型变体, 第二和第三个ICPS将使用 RL10 C-2型变体。[55][56][57] Block 1型能够拥有95 t(93 long ton;105 short ton)的近地轨道运载能力,包括作为有效载荷一部分的ICPS重量。[4]阿耳忒弥斯1号任务中,当火箭的核心级分离后,有效载荷将处在1,806乘30 km(1,122乘19 mi) 的亚轨道上,这便于核心级的安全处置。[58] 然后ICPS将执行轨道注入和随后的地月转移,把猎户座飞船送往月球。[59] ICPS将为阿耳忒弥斯2、3号的载人飞行提供乘员认证。[54]

探索上面级(EUS)计划在阿耳忒弥斯4号及之后的任务中使用,EUS将完成上升阶段然后进行深空轨道注入。[60] EUS将在太空發射系統的Block 1B和Block 2型上使用,其直径与核心级相同为8.4米,由四台RL-10 C3引擎提供动力,最终将升级为使用四个改进的RL10 C-X引擎。[61][62] 截至2022年3月 (2022-03), 波音正在为 EUS 开发一种新的基于复合材料的燃料箱,这将使Block 1B型的地月轨道有效载荷能力增加 30%。[63] 探索上面级(EUS)原先的名称是双用途上面级(DUUS),相对于ICPS是专门为太空發射系統开发的上面级。[60][64]

变体

太空發射系統不同型号之间的差异
发射序号# 型号 核心级引擎 助推器 上面级 起飞推力 酬載量
近地轨道 (LEO) 地月转移 (TLI) 日心轨道 (HCO)
1 1 RS-25D[39] 五段式固体火箭助推器 临时低温推进上级 (ICPS) RL-10B-2引擎[57] 39 MN(8,800,000 lbf[8] 95 metric ton(209,000磅)[4] >27 metric ton(59,500磅)[65][8][9] 未知
2, 3 临时低温推进上级 (ICPS) RL10C-2引擎[55]
4 1B 探索上面级 (EUS)

4台RL10火箭发动机

105 metric ton(231,000磅)[5] 42 metric ton(92,500磅)[65][8][9]
5,6,7,8 RS-25E[44]
9, ... 2 助推器报废和延长寿命计划 (BOLE)[50] 41 MN(9,200,000 lbf)[8] 130 metric ton(290,000磅)[7] >46 metric ton(101,400磅)[65][8][9] 45 metric ton(99,000磅)[4]

發展

太空發射系統是一種從太空梭演變而來的重型運載火箭。第一階段以载重量70噸的星座計劃載人任務為主,发射時將產生3810吨的推力;再發展出载重量130噸的貨艙型酬載任務,發射推力约合4173噸,高度和總重量将分别為117公尺和2948噸。[66][67]

初步設計顯示,太空梭主發動機太空梭固態助推器都會被作為本計畫的一部分。不像戰神五號運載火箭需要另外開發新的燃料槽[67]

沿用太空梭系統的新飛船

2011年5月,美國國家航空暨太空總署宣布將已取消的星座計畫中的獵戶座飞船繼續開發,並命名為多功能人員酬載艙[68]。在2011年9月所公布的資料顯示,第一階段載人任務會使用一對太空梭固態助推器以及三顆太空梭主發動機的改進版本(RS-25D/E),第二節則選用J-2X發動機[69][70]。第二階段貨艙任務會使用一對太空梭固態助推器的加強版以及五顆太空梭主發動機的改進版本(RS-25D/E)[70]

2011年9月14日,美國國家航空暨太空總署確定新一代太空發射系統的設計,並說明美國可以將太空人運送到更遠的地方,並且做為人類太空探測的基石[71][72][73]

重視資金運用

太空發射系統預計花費180億美元開發,2012年至2017年間,每年將編列30億美元的預算;其中100億美元用於太空發射系統本身:20億美元改建發射台及甘迺迪太空中心:60億美元用於獵戶座載人艙組的研究、製作[74]。根据美國太空總署的預算,从2014年到2017年首次試射前,建造測試版本的SLS火箭需要投入约70億美元。到2019年,經費投入将達到180亿美元左右,而这筆資金還只是用於研發和設計,並不涵蓋火箭的製造成本。新型火箭研製計畫的總估计投入將達到360億美元。

在 2011 年 9 月的參議院與美國國家航空航天局聯合介紹中,據稱到 2017 年 SLS 計劃的預計開發成本為 美元180 億美元,其中 100 億美元用於 SLS 火箭,60 億美元用於獵戶座飛船,以及 20 億美元用於升級 肯尼迪航天中心 的發射台和其他設施。[75][76] Booz Allen Hamilton 為 NASA 撰寫的 2011 年獨立成本評估報告中,這些成本和時間表被認為是樂觀的。[77] 2011 年 NASA 的一份內部文件估計,到 2025 年,四次 95 t(93 long ton;105 short ton) 發射(1 次無人駕駛,3 次載人)的計劃總成本至少為 410 億美元,[78][79] 130 t(130 long ton;140 short ton) 版本準備不早於 2030 年。[80] 人類探索團隊估計 2010 年 Block 0 的單位成本為 16 億美元,Block 1 的單位成本為 18.6 億美元。[81] 然而,自從做出了這些估計,Block 0 SLS 車輛在 2011 年底被放棄,設計沒有完成。[32]

2012 年 9 月,SLS 項目副經理表示,5 億美元是 SLS 計劃每次飛行的合理目標平均成本。[82] 2013 年,《太空評論》估計每次發射的成本為 50 億美元,具體取決於發射費用。[83][84] NASA 於 2013 年宣布 歐洲太空總署 將建造 獵戶座服務艙[85] 2014 年 8 月,隨著 SLS 計劃通過關鍵決策點 C 審查並進入全面開發階段,從 2014 年 2 月到計劃於 2018 年 9 月啟動的成本估計為 70.21 億美元。[86] 同時,地面系統的修改和建設將需要額外的 18 億美元。[87]

2018 年 10 月,NASA 監察長 報告稱,截至 2018 年 8 月,波音 核心階段合同已佔 SLS 支出 119 億美元的 40%。到 2021 年,核心預計各階段耗資 89 億美元,是最初計劃金額的兩倍。[88] 2018 年 12 月,NASA 估計 SLS 的年度預算在 2019 年至 2023 年之間將在 21 至 23 億美元之間。[89]

2019 年 3 月,特朗普政府 向 NASA 發布了 2020 財年預算申請。該預算不包括用於 SLS Block 1B 和 Block 2 的任何資金。因此不確定是否會開發這些 SLS 的未來變體,但國會的行動在通過的預算中恢復了這筆資金。[90] 之前為 SLS Block 1B 計劃的幾次發射預計將在商業運載火箭上飛行,例如 獵鷹重型火箭新葛倫火箭火神火箭[91] 然而,要求為 SLS、獵戶座飛船和載人著陸器增加 16 億美元的預算以及發射清單似乎表明支持 Block 1B 的開發,即 Artemis 3 的首次亮相。Block 1B 將主要用於共同載人的機組人員轉移和後勤需求,而不是建造門戶。無人駕駛的 Block 1B 計劃於 2028 年發射月球表面資產,這是 Artemis 計劃的第一個月球前哨基地。2022年3月17日傍晚6時許,組裝完成的太空發射系統,由太空梭運輸車(Crawling Transporter)緩慢運出飛行器裝配大樓;並將花費11個小時的時間運往6.4公里外的甘迺迪太空中心 39B 發射台上,進行火箭濕式演練(Wet Dress Rehearsal,WDR)。[92]

預算編列

2011至2021財年,SLS計劃名義資金總額為212.09億美元。這相當於2021年通脹後的230.11億美元。[93]

財年 資金 狀態
標稱
(百萬美金)
2021年[93]
(百萬美金)
2011 $1,536.1 $1,829.5 實際[94]
(Formal SLS Program reporting excludes the Fiscal 2011 budget.)[95]
2012 $1,497.5 $1,765.6 實際[96]
2013 $1,414.9 $1,642.7 實際[97]
2014 $1,600.0 $1,822.4 實際[98]
2015 $1,678.6 $1,873.3 實際[99]
2016 $1,971.9 $2,171.7 實際[100]
2017 $2,127.1 $2,299.4 實際[101]
2018 $2,150.0 $2,268.3 實際[102]
2019 $2,150.0 $2,233.1 實際[103]
2020 $2,528.1 $2,561.0 實際[104]
2021 $2,555.0 $2,555.0 頒布[105]
總計:2011–2021 $21,209.2 $23,011.2

SLS 的生產和運營成本為 22 億美元,探索地面系統(英語:Exploration Ground Systems) 的生產和運營成本為 5.68 億美元。此外,由於前四次任務屬於 Artemis 計劃,獵戶座飛船的有效載荷將花費 10 億美元,歐洲服務艙將花費 3 億美元。:23

早期計劃 2018年SLS的計劃演化 2015 年 3 月在猶他州奧格登西北部的 Orbital ATK 沙漠設施進行的 SLS 助推器測試 探索地面系統 和 Jacobs 準備提升和放置 SLS 火箭的核心級,2021 年 6 月

SLS 是根據 2010 年國會法案(公法 111-267)創建的,其中指示 NASA 創建一個系統,用於將有效載荷和機組人員發射到太空,以取代因航天飛機退役而喪失的能力。該法案設定了某些目標,例如能夠將 130 噸或更多的有效載荷提升到近地軌道,目標日期為 2016 年 12 月 31 日系統全面運行,以及“在可行範圍內”使用的指令” 航天飛機和戰神 1 號的現有組件、硬件和勞動力, 12 2011 年 9 月 14 日,NASA 宣布了滿足這些要求的計劃:SLS 的設計,獵戶座飛船作為有效載荷。

SLS 已經考慮了幾種潛在發射配置的未來發展路線,火箭模塊的計劃演進已被多次修改。考慮了許多選項,所有這些選項都只需要滿足國會規定的最低有效載荷,包括具有三個主引擎的 Block 0 變體,具有五個主引擎的變體,具有升級助推器而不是改進的第二階段的 Block 1A 變體, Block 2 有五個主引擎加上地球出發階段,最多有三個 J-2X 引擎。

在 SLS 設計的最初公告中,NASA 還宣布了“高級助推器競賽”,以選擇將在 SLS 的 Block 2 上使用哪些助推器。幾家公司為這次比賽提出了助推器,所有這些都被證明是可行的,洛克達因泰萊迪布朗工程 提出了三個助推發動機,每個發動機都帶有雙燃燒室,ATK 提出了一種改進的固體火箭助推器,它具有更輕的外殼、更高能的推進劑和四個部分五,普惠洛克達因提出了一種名為 Pyrios 的液體燃料助推器。然而,本次競賽是為一項開發計劃而設計的,在該計劃中,Block 1A 之後是 Block 2A,並帶有升級的助推器。美國國家航空航天局在 2014 年 4 月取消了 Block 1A 和計劃中的競賽,支持簡單地保留戰神 I 的五段固體火箭助推器,它們本身是從航天飛機的固體火箭助推器改裝而來的,至少到 2020 年代後期。過於強大的先進助推器會導致不合適的高加速度,並且需要對 LC-39B、它的火焰溝槽和移動發射器進行修改。

2013 年 7 月 31 日,SLS 通過了初步設計審查。審查不僅包括火箭和助推器,還包括地面支持和後勤安排。

2014 年 8 月 7 日,SLS Block 1 通過了一個稱為關鍵決策點 C 的里程碑並進入全面開發,預計發射日期為 2018 年 11 月。

EUS期權

2013 年,NASA 和波音公司分析了幾種 EUS 發動機選項的性能。該分析基於 105 公噸的第二級可用推進劑負載,並將各級與四台 RL10 發動機、兩台 MARC-60 發動機或一台 J-2X 發動機進行比較。 2014 年,NASA 還考慮使用歐洲 Vinci 代替 RL10,後者提供相同的比衝但推力增加 64%,這將以更低的成本實現相同的性能。

2018 年,藍色起源提交了一份提案,用公司設計和製造的更便宜的替代品取代探索上層,但該提案於 2019 年 11 月被 NASA 以多種理由拒絕;其中包括與現有 EUS 設計相比性能較低,該提案與車輛裝配大樓門的高度僅為 390 英尺不兼容,以及 獵戶座飛船 組件(如太陽能電池板)的加速度不可接受。:7-8

SRB測試

2009年至2011年,星座計劃對五段式固體火箭助推器進行了3次全時程靜態點火試驗,包括低核心溫度和高核心溫度測試,以驗證極端溫度下的性能。 5 段固體火箭助推器將轉移到 SLS。 Northrop Grumman Innovation Systems 已經完成了五段固體火箭助推器的全持續時間靜態點火測試。合格電機 1 於 2015 年 3 月 10 日進行了測試。合格電機 2 於 2016 年 6 月 28 日成功進行了測試。

上表包含的項目包括SLS的臨時上部階段,即臨時低溫推進階段 (ICPS),其中包括 4.12 億美元的合同。[106]

表中還包括開發Exploration Upper Stage英语Exploration Upper Stage的成本:

財年 開發EUS英语Exploration Upper Stage的資金
標稱
(百萬美金)
2021年[93]
(百萬美金)
2016 $77.0[100] $84.8
2017 $300.0[107][101] $324.3
2018 $300.0[108][102] $316.5
2019 $150.0[109][103] $155.1
2020 $300.0[104] $303.9
2021 $400.0[105][註 3] $400.0
Total: 2016–2021 $1,527.0 $1,584.6

啟動成本

對 SLS 每次發射成本的估計差異很大,部分原因是不確定該計劃在運營發射開始前的開發和測試期間將花費多少,部分原因是各機構使用不同的成本衡量標準;但也基於成本估算的不同目的。例如,每增加一次發射的邊際成本忽略開發和年度經常性固定成本,而每次發射的總成本包括經常性成本但不包括開發。

對於 SLS 每次發射的成本,以及 SLS 項目投入運營後每年的經常性成本,NASA 都沒有官方的估計。每次發射的成本不是一個直接估計的數字,因為它在很大程度上取決於每年發射的次數。[1] 例如,類似地,航天飛機 的估計值是 2012 年的美元,如果每年能夠實現 7 次發射,則每次發射的成本為 5.76 億美元,而在給定年份增加一次額外發射的邊際成本估計不到其一半,邊際成本僅為 2.52 億美元。然而,按照它的飛行速度,包括開發在內的每次航天飛機發射的最終成本為 16.4 億美元。[110]:III−490

NASA 副局長 William H. Gerstenmaier 在 2017 年表示,不會對 NASA 為 SLS 提供的任何品種的每次飛行成本進行官方估算。[111] 其他機構,例如 政府問責辦公室 (GAO)、NASA 監察長辦公室參議院撥款委員會,以及 美國國家航空航天局監察長辦公室然而,管理和預算|白宮管理和預算辦公室]]已經公佈了每次發射的成本數據。 NASA 的幾個內部計劃和項目概念研究報告已經發布了包括未來 SLS 發射在內的擬議預算。例如,一份太空望遠鏡的概念研究報告稱,NASA 總部在 2019 年建議為 2035 年的 SLS 發射預算 5 億美元。[112] 2019 年的另一項研究也提出了太空望遠鏡的設想,他們的發射預算以當前美元計算為 6.5 億美元,或者發射時間為 9.25 億美元,也就是“2030 年代中期”。[113]

Europa Clipper 是 NASA 的一項科學任務,最初是國會要求在 SLS 上發射的。 NASA 內部和外部的監督機構都不同意這一要求。首先,美國宇航局監察長辦公室於2019年5月發布了一份報告[114][115] 這表明 Europa Clipper 需要為 SLS 發射的“邊際成本”放棄 8.76 億美元。然後,2019 年 8 月發布的這封信的附錄增加了估計,並表示改用商用火箭將節省超過 10 億美元。但是,這些節省可能包括與發射計劃延遲相關的部分費用;商業替代品可能會比 SLS 更早推出。

該信中引用的 JCL(聯合成本和進度置信水平)分析表明,每次發射節省的成本為 7 億美元,其中 SLS 每次發射 10.5 億美元,商業替代方案為 3.5 億美元。[116][117] 最後,白宮管理和預算辦公室 (OMB) 於 2019 年 10 月致參議院撥款委員會的一封信顯示,SLS 在開發完成後每次發射對納稅人的總成本估計為“超過 20 億美元”;表示,按 2021 年的美元計算,開發成本為 230 億美元。[118][註 4] 這封信建議國會取消這一要求,同意 NASA 監察長的意見,並補充說,使用 Europa Clipper 的商業運載火箭而不是 SLS 將總共節省 15 億美元。 NASA 沒有否認這 20 億美元的發射成本,該機構發言人表示,「隨著該機構繼續與波音公司就長期生產合同和努力進行談判,它正在努力降低給定年份單次 SLS 發射的成本確定火箭其他部件的合同和成本」。[1]

OMB 的這個數字取決於建造速度,因此更快地建造更多 SLS 火箭可以降低單位成本。[1] 例如,探索地面系統其唯一作用是支持、組裝、集成和發射 SLS——已單獨預算每年 6 億美元的設施固定成本,無論當年發射多少火箭。[119] 然後,在 2019 年 12 月,NASA 局長 Jim Bridenstine 非正式地表示,他不同意 20 億美元的數字,因為 SLS 發射的邊際成本應該會在前幾次發射後下降,預計最終將達到 8 億至 900 美元左右萬,儘管合同談判才剛剛開始。[120]

然後,在 2021 年 7 月,NASA 宣布將使用 SpaceX 獵鷹重型火箭 代替 SLS 來發射 Europa Clipper。[121] 這樣做是出於與成本無關的技術原因,總成本節省估計為 20 億美元。[122][123][124]

2021 年 11 月,發布了一項新的 NASA 監察長辦公室 審計,估計至少對於 SLS 的前四次發射,SLS 每次發射的生產和運營成本為 22 億美元,外加 568 美元百萬用於 探索地面系統。此外,由於前四次任務是在 Artemis 計劃下進行的,獵戶座飛船 的有效載荷將花費 10 億美元,ESA 服務模塊將花費 3 億美元。[125]:23

早期計劃

 
2018年SLS的計劃演變
2015 年 3 月在猶他州奧格登西北部的 Orbital ATK 沙漠設施進行的 SLS 助推器測試
2021 年 6 月,探索地面系統 和 Jacobs 準備提升和放置 SLS 火箭的核心級

SLS 是由國會在 2010 年通過的一項公法 111-267 創建的,其中指示 NASA 創建一個系統,用於將有效載荷和機組人員發射到太空,以取代因 航天飛機退役而失去的能力.[30] 該法案設定了某些目標,例如能夠將 130 噸或更多的有效載荷提升到近地軌道,目標日期為 2016 年 12 月 31 日系統全面運行,以及“在可行範圍內”使用的指令“來自航天飛機和 戰神1號 的現有組件、硬件和勞動力。[30]:12 2011 年 9 月 14 日,NASA 宣布了滿足這些要求的計劃:SLS 的設計,以 獵戶座飛船 作為載荷。[126][127][128][129]

SLS 已經考慮了幾種潛在發射配置的未來發展路線,火箭模塊的計劃演進已被多次修改。[130] 考慮了很多選項,所有這些都只需要滿足國會規定的最低有效載荷,[130] 包括具有三個主要引擎的 Block 0 變體,[32] 具有五個主引擎的變體,[130] 具有升級助推器而不是改進的第二節的 Block 1A 變體,[32] Block 2 有五個主引擎加上 地球出發階段(英語:Earth Departure Stage),最多有三個 J-2X 引擎。[35]

在 SLS 設計的最初公告中,NASA 還宣布了“高級助推器競賽”,以選擇將在 SLS 的 Block 2 上使用哪些助推器。[126][70][37][131] 幾家公司為本次比賽提出了助推器,所有這些都被證明是可行的,[132] 洛克達恩Teledyne Brown 提出了三個增壓發動機,每個發動機都有雙燃燒室,[133] Alliant Techsystems 提出了一種改進的固體火箭助推器,具有更輕的外殼、更高能的推進劑和四段反而不是五段,[134] Pratt & Whitney RocketdyneDynetics 提出了一種名為 Pyrios 的液體燃料助推器。[135] 然而,本次競賽是為一項開發計劃而設計的,在該計劃中,Block 1A 之後是 Block 2A,並帶有升級的助推器。 NASA 在 2014 年 4 月取消了 Block 1A 和計劃中的競賽,支持簡單地保留 戰神1號 的五段固體火箭助推器,它們本身是從 航天飛機 的固體火箭助推器改裝而來的,至少到 2020 年代後期。[130][136] 過於強大的先進助推器會導致對人體不合適的加速度,並且需要修改 LC-39B、它的火焰溝槽和 移動發射器.[137][130]

2013 年 7 月 31 日,SLS 通過了初步設計審查。審查不僅包括火箭和助推器,還包括地面支持和後勤安排。[138]

2014 年 8 月 7 日,SLS Block 1 通過了一個稱為關鍵決策點 C 的里程碑並進入全面開發,預計發射日期為 2018 年 11 月。[86][139]

EUS 選項

2013 年,NASA 和波音公司分析了幾種 EUS 發動機選項的性能。該分析基於 105 公噸的第二級可用推進劑負載,並比較了四台 RL10 發動機、兩台 MARC-60 發動機或一台 J-2X 發動機的階段。[140][141] 2014 年,NASA 還考慮使用歐洲的 Vinci 代替 RL10,它提供相同的比衝但推力大 64%,這將以更低的成本換取相同的性能。[142]

2018 年,Blue Origin 提交了一份提案,用公司設計和製造的更便宜的替代品取代SLS第二級(探索上層級),但該提案於 2019 年 11 月被 NASA 以多種理由拒絕;其中包括與現有 EUS 設計相比性能較低,提案與 車輛裝配大樓 門的高度僅為 390 英尺不兼容,以及太陽能電池板等獵戶座飛船組件的加速度不能接受。[143][144]:7–8

固體火箭助推器(SRB)測試

從 2009 年到 2011 年,在 星座計劃 下,對五節固體火箭助推器進行了 3 次全持續時間靜態點火試驗,包括低核心溫度和高核心溫度測試,以驗證極端溫度下的性能。[145][146][147] 5 段式固體火箭助推器將由 SLS 使用。[130] Northrop Grumman Innovation Systems 已經完成了五段固體火箭助推器的全持續靜態點火測試。Qualification Motor 1 於 2015 年 3 月 10 日進行了測試。[148] Qualification Motor 2 於 2016 年 6 月 28 日成功通過測試。[149]

測試和計畫

 
2018年SLS的計劃演變
已隱藏部分未翻譯内容,歡迎參與翻譯

建設

 
Liquid hydrogen tank for Artemis 2 under construction, as of August 2020
 
"Boat-tail" for Artemis 2 under construction, as of June 2021
 
Engine section shroud structure for Artemis 3 under construction, as of April 2021

截至2020年 (2020-Missing required parameter 1=month!), 已計畫了三個太空發射系統的版本: Block 1、Block 1B和Block 2. 它們都採用相同的核心級與4個主引擎, 但Block 1B將使用探索上層級(EUS), 而Block 2將會採用探索上層級與升級的助推器, 也就是推進器報廢和延長壽命計劃(BOLE).[150][5][151]

在2017年七月聯合發射聯盟已交付給NASA臨時低溫推進上級(ICPS), 且2018年11月起已安置在甘迺迪太空中心.[152].[153]

Construction of core stage

In mid-November 2014, construction of the first Core Stage hardware began using a new welding system in the South Vertical Assembly Building at NASA's Michoud Assembly Facility.[154] Between 2015 and 2017, NASA test fired RS-25 engines in preparation for use on SLS.[43]

The core stage for the first SLS, built at Michoud Assembly Facility by Boeing,[155] had all four engines attached in November 2019,[156] and it was declared finished by NASA in December 2019.[157]

The first core stage left Michoud Assembly Facility for comprehensive testing at Stennis Space Center in January 2020.[158] The static firing test program at Stennis Space Center, known as the Green Run, operated all the core stage systems simultaneously for the first time.[159][160] Test 7 (of 8), the wet dress rehearsal, was carried out in December 2020 and the fire (test 8) took place on 16 January 2021, but shut down earlier than expected,[161] about 67 seconds in total rather than the desired eight minutes. The reason for the early shutdown was later reported to be because of conservative test commit criteria on the thrust vector control system, specific only for ground testing and not for flight. If this scenario occurred during a flight, the rocket would have continued to fly normally. There was no sign of damage to the core stage or the engines, contrary to initial concerns.[162] The second fire test was completed on 18 March 2021, with all 4 engines igniting, throttling down as expected to simulate in-flight conditions, and gimballing profiles. The core stage was shipped to Kennedy Space Center to be mated with the rest of the rocket for Artemis 1. It left Stennis on April 24 and arrived at Kennedy on April 27.[163] It was refurbished there in preparation for stacking.[164] On 12 June 2021, NASA announced the assembly of the first SLS rocket was completed at the Kennedy Space Center. The assembled SLS is planned to be used for the uncrewed Artemis 1 mission in 2022.[165]

While the first SLS for Artemis 1 is being prepared for launch, NASA and Boeing are constructing the next three, for Artemis 2, Artemis 3, and Artemis 4.[166] Boeing stated in July 2021 that while the COVID-19 pandemic has affected their suppliers and schedules, such as delaying parts needed for hydraulics, they still will be able to provide the Artemis 2 SLS Core stage per NASA's schedule, with months to spare.[166] The spray-on foam insulation process for Artemis 2 has been automated since Artemis 1 for most sections of the core stage, saving 12 days in the schedule.[167][166] The Artemis 2 forward skirt, which is the foremost component of the Core stage, was affixed on the liquid oxygen tank in late May 2021.[166] 截至2022年7月 (2022-07), is set to ship to NASA in March 2023.[168] Artemis 3, assembly elements of the thrust structure began at Michoud Assembly Facility in early 2021.[166] The liquid hydrogen tank that is to be used on Artemis 3 was originally planned to be the Artemis 1 tank, but it was set aside as the welds were found to be faulty.[169]:2 Repair techniques were developed, and the tank has reentered production and will be proof tested for strength, for use on Artemis 3.[169]:2

Construction of EUS for Block 1B

As of July 2021, Boeing is also preparing to begin construction of the Exploration Upper Stage (EUS), which is planned to debut on Artemis 4.[166]

Planned launches

Originally planned for late 2016, the uncrewed first flight of SLS has slipped more than sixteen times and more than five years.[註 2] As of July 2022, NASA projects the SLS will launch no earlier than 29 August 2022.[192] NASA limits the amount of time the solid rocket boosters can remain stacked to "about a year" from the time two segments are joined.[193] The first and second segments of the Artemis 1 boosters were joined on 7 January 2021.[194] NASA can choose to extend the time limit based on an engineering review.[195] On 29 September 2021, Northrop Grumman indicated that the limit can be extended to eighteen months for Artemis 1, based on an analysis of the data collected when the boosters were being stacked.[165] In late 2015, the SLS program was stated to have a 70% confidence level for the first Orion flight that carries crew, the second SLS flight overall, by 2023;[196][197][198] 截至November 2021年 (November 2021-Missing required parameter 1=month!), NASA delayed Artemis 2 from 2023[199] to May 2024.[200] Template:SLS launches/future

Usage beyond Artemis

While the SLS is only confirmed for use on the first few Artemis missions, many NASA mission concept studies for robotic missions planned to launch on the SLS, such as: Neptune Odyssey,[201][202] Europa Lander,[203][204][205] Enceladus Orbilander, Persephone,[206] HabEx,[113] Origins Space Telescope,[112] LUVOIR,[207] Lynx,[208] and Interstellar probe.[209] These concept studies were prepared for possible recommendation by the National Academy's Decadal surveys. The Astronomy and Astrophysics Decadal Survey in 2021 recommended a smaller, merged version of HabEx and LUVOIR preceded by a technology maturation program to reduce cost and schedule risk, although the eventual mission may or may not use SLS. In 2022 the Planetary Science Decadal Survey recommended Enceladus Orbilander as the third highest priority for flagship planetary missions in the 2020s. The Heliophysics Decadal Survey, due to be completed in 2024, is considering the Interstellar Probe mission concept.

2021年1月16日,美國太空總署斯坦尼斯航天中心測試太空發射系統的引擎,不過引擎啟動僅1分鐘後就因技術問題提前熄滅,而搜集所需數據至少需要啟動4分鐘[210]

2021年3月19日,美國太空總署斯坦尼斯航天中心測試太空發射系統的引擎,並完成8分鐘靜態點火測試。

2022年3月18日,太空發射系統轉移至甘迺迪太空中心39B發射台,預備進行燃料加注測試。

2022年8月3日,美國太空總署發佈Artemis-1任務詳情,並暫定8月29日 8:33ET發射。

2022年8月29日上午,已加注完推進劑的太空發射系統,核心級(Core Stage)的1具RS-25發動機冷卻管線出現液氫洩漏。由於無法即時解決問題,NASA在倒數暫停於40分鐘許久之後宣布取消發射,並延後至9月2日的第2個發射窗口(Launch Window)。

2022年9月3日早上,已加注完液態氧的太空發射系統,由於地面設施中的快速斷開連接臂(Quick Disconnect Arm)泄漏液態氫,空氣中氫氣濃度過高而終止加注燃料,發射倒數暫停於T-2:28:53。最後,NASA官方宣布取消此次發射任務,並延後至之後的發射窗口(Launch Window),以便修復設施。

2022年9月26日,為避免火箭受颶風伊恩(Ian)吹襲而損毀,美國太空總署決定將太空發射系統送返垂直組裝大樓,亦代表下次發射窗口將不早於2022年11月。

2022年11月8日,美國太空總署因應颶風妮可(Nicole)吹襲佛羅里達州,將發射時間由11月14日推遲至11月16日[211]

2022年11月16日,太空發射系統於甘迺迪太空中心39B發射台順利升空,獵戶座號並進入預定軌道。[212][213]

一個非官方與非正式的單位在預算的最壞狀態列出一些太空發射系統的早期發射排程[214]

 
美國國家航空暨太空總署的太空發射系統從2011年2月時的參考配置
任務 組合 當前狀態 發射时间 目標 備注
Artemis-1 Block 1 (不載人) 成功 2022年11月16日1:47:44 (EST) 6:47:44 (UTC) 將不載人的獵戶座太空船進行飛掠月球2次的任務。 第一次發射嘗試因閥門異常導致三號發動機未能達到目標溫度而推遲
第二次發射嘗試因快速斷開連接裝置泄漏液態氫而中止,加上受颶風威脅,SLS運返VAB作進一步檢查。
第三次發射嘗試因颶風威脅而推遲至11月16日。
最終Artemis-1成功於11月16日發射,獵戶座號成功進入預定軌道,並按原定計劃順利返回地球。
Artemis-2 Block 1 (載人) 建造中 不早於2024年11月 太空人將乘坐獵戶座太空船進行飛掠月球的任務。
Artemis-3 Block 1 (載人) 建造中 預計2025年 太空人將乘坐獵戶座太空船於月球軌道與人類登陸系統(SpaceX星艦)會合,並進行登月任務。
Artemis-4 Block 1B (載人及載貨) 建造中 預計2026年 將發射月球門戶模組,並由太空人進行軌道會合
Artemis-5 Block 1B (載人及載貨) 已計劃 預計2027年 將發射月球門戶模組及月球探索運輸系統,並由太空人進行相關任務。

批評

SLS因計劃成本、进展缓慢、缺乏商業參與、立法使用航天飛機組件飛行器的非競爭性而受到批評。

已隱藏部分未翻譯内容,歡迎參與翻譯

資金

In 2011, Rep. Tom McClintock and other groups called on the Government Accountability Office to investigate possible violations of the Competition in Contracting Act, arguing that Congressional mandates forcing NASA to use Space Shuttle components for the SLS are de facto non-competitive, single-source requirements assuring contracts to existing Shuttle suppliers.[215][216][217] The Competitive Space Task Force, in September 2011, said that the new government launcher directly violates NASA's charter, the Space Act, and the 1998 Commercial Space Act requirements for NASA to pursue the "fullest possible engagement of commercial providers" and to "seek and encourage, to the maximum extent possible, the fullest commercial use of space".[218][217] Opponents of the heavy launch vehicle have critically used the name "Senate launch system",[56][217][219]a name that was still being used by opponents to criticize the program in 2021, as "the NASA Inspector General said the total cost of the rocket would reach $27 billion through 2025".[220]

Lori Garver, a former NASA Deputy Administrator, called for canceling the launch vehicle alongside the Mars 2020 rover.[221] Phil Plait shared his criticism of the SLS in light of ongoing budget tradeoffs between the Commercial Crew Development and SLS budgets, also referring to earlier critiques by Garver.[222] In 2019, the Government Accountability Office found that NASA had awarded Boeing over $200 million for service with ratings of good to excellent despite cost overruns and delays. 截至2019年 (2019-Missing required parameter 1=month!), the maiden launch of the SLS was expected in 2021.[223][224] NASA continued to expect that the first orbital launch would be in 2021 as late as May 2021.[182]

 
Visual from the March 2020 Inspector General report, showing how NASA used accounting to "mask" a cost increase by moving the boosters (which cost $889 million) from the SLS to another cost center, without updating the SLS budget to match[225]:iv,22

NASA moved out $889 million of costs relating to SLS boosters, but did not update the SLS budget to match, a March 2020 Inspector General report found. This kept the budget overrun to 15% by FY 2019.[225]:22 At 30%, NASA would have to notify Congress and stop funding unless Congress reapproves and provides additional funding.[225]:21–23 The Inspector General report found that were it not for this "masking" of cost, the overrun would have been 33% by FY 2019.[225]:iv,23 The GAO separately stated "NASA's current approach for reporting cost growth misrepresents the cost performance of the program".[226]:19–20

On 1 May 2020, NASA awarded a contract extension to Aerojet Rocketdyne to manufacture 18 additional RS-25 engines with associated services for $1.79 billion, bringing the total RS-25 contract value to almost $3.5 billion.[227][44] Ars Technica commented that the average cost of each RS-25 therefore rose to $146 million, so each SLS launch uses $580 million for its four engines. Ars noted that for the cost of just one engine, six more powerful RD-180 engines could be purchased, or nearly an entire Falcon Heavy launch with two-thirds of the SLS lift capacity.[227][228] Former NASA Administrator Charlie Bolden, who oversaw the initial design and development of the SLS, also criticized of the program in an interview with Politico in September 2020. Bolden said that the "SLS will go away ... because at some point commercial entities are going to catch up." Bolden further stated, "They are really going to build a heavy-lift launch vehicle sort of like SLS that they will be able to fly for a much cheaper price than NASA can do SLS. That's just the way it works."[229]

建議的替代方案

 
Space Launch System and Falcon 9 at Launch Complex 39, the former is preparing for the Axiom Mission 1, and the latter for the Artemis 1 mission.

In 2009, the Augustine commission proposed a commercial 75 t(83 short ton) launcher with lower operating costs and noted that a 40—60 t(44—66 short ton) launcher was the minimum required to support lunar exploration.[230] In 2011–2012, the Space Access Society, Space Frontier Foundation, and The Planetary Society called for the cancellation of the project, arguing that the SLS will consume the funds for other projects from the NASA budget.[218][215][231] U.S. Representative Dana Rohrabacher and others proposed that an orbital propellant depot should be developed and the Commercial Crew Development program accelerated instead.[218][232][233][234][235]

A NASA study that was not publicly released[236][237] and another from the Georgia Institute of Technology showed this option to be possibly cheaper.[238][239] In 2012, the United Launch Alliance also suggested using existing rockets with on-orbit assembly and propellant depots as needed. The lack of competition in the SLS design was highlighted.[240][241][242][219][243] In the summer of 2019, a former ULA employee claimed that Boeing, NASA's prime contractor for SLS, viewed orbital refueling technology as a threat to the SLS and blocked further investment in it.[244] In 2011, Robert Zubrin, founder of Mars Society and Mars Direct, suggested that a heavy lift vehicle could be developed for $5 billion on fixed-price requests for proposal.[245] In 2010, SpaceX's CEO Elon Musk claimed that his company could build a launch vehicle in the 140—150 t(310,000—330,000磅) payload range for $2.5 billion, or $300 million (in 2010 dollars) per launch, not including a potential upper-stage upgrade.[246][247]

助推器測試相關

備註

  1. ^ 200-km (124-mi) altitude, 28.5° inclination, circular[3]
  2. ^ 2.0 2.1
    Then-planned launch date history
    Date Planned launch date
    October 2010 31 December 2016[30][22][170][171]
    September 2011 2017[172][173][171]
    August 2014 December 2017[171]
    December 2014 June - July 2018[174]
    13 April 2017[矛盾] November 2018[175]
    28 April 2017 2019[176][171]
    November 2017 June 2020[177]
    December 2019 November 2020[178][179]
    21 February 2020 18 April 2021[179]
    28 February 2020 Mid to late 2021[180]
    May 2020 22 November 2021[181][182]
    August 2021 December 2021[183][184]
    22 October 2021 12 February 2022[185][186]
    17 December 2021 March - April 2022[187]
    February 2022 May 2022[188]
    March 2022 June 2022[189]
    26 April 2022 23 August 2022[190][191]
    20 July 2022 8:33 am ET (12:33 UTC), 29 August 2022[192]
  3. ^ The FY2021 spending plan indicates that this is for "Block 1B (non-add) (including EUS)"
  4. ^ 引用错误:没有为名为totalcost的参考文献提供内容

參考

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  168. ^ Sloss, Philip. Boeing aiming to deliver second SLS Core Stage to NASA in March. NASASpaceFlight.com. 2022-07-25 [2022-07-30]. (原始内容存档于2022-08-31) (美国英语). 
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  211. ^ https://twitter.com/NASA/status/1590116388403785729页面存档备份,存于互联网档案馆) SLS Launch delayed to 16th Nov
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  225. ^ 225.0 225.1 225.2 225.3 NASA'S MANAGEMENT OF SPACE LAUNCH SYSTEM PROGRAM COSTS AND CONTRACTS (PDF). NASA – Office of Inspector General – Office of Audits. 2020-03-10 [2020-09-14]. (原始内容存档 (PDF)于2020-08-28). Based on our review of SLS Program cost reporting, we found that the Program exceeded its Agency Baseline Commitment (ABC) by at least 33 percent at the end of FY 2019, a figure that could reach 43 percent or higher if additional delays push the launch date for Artemis I beyond November 2020. This is due to cost increases tied to Artemis I and a December 2017 replan that removed almost $1 billion of costs from the ABC without lowering the baseline, thereby masking the impact of Artemis I’s projected 19-month schedule delay from November 2018 to a June 2020 launch date. Since the replan, the SLS Program now projects the Artemis I launch will be delayed to at least spring 2021 or later. Further, we found NASA’s ABC cost reporting only tracks Artemis I-related activities and not additional expenditures of almost $6 billion through FY 2020 that are not being reported or tracked through the official congressional cost commitment or the ABC. [...] as a result of delaying Artemis I up to 19 months to June 2020, NASA conducted a replan of the SLS Program in 2017 and removed $889 million in Booster and RS-25 Engine-related development costs because SLS Program officials determined those activities were not directly tied to Artemis I. [...] In our judgement, the removal of these costs should have reduced the SLS Program’s ABC development costs from $7.02 billion to $6.13 billion. [...] SLS Program and HEOMD officials disagreed with our assessment and stated the SLS Program’s change in cost estimates for the Booster and Engines element offices were not a removal of costs but rather a reallocation of those activities to appropriately account for them as non-Artemis I costs. [...] Federal law requires that any time Agency program managers have reasonable knowledge that development costs are likely to exceed the ABC by more than 30 percent, they must notify the NASA Administrator. Once the Administrator determines the SLS Program will exceed the development cost baseline by 30 percent or more, NASA is required to notify Congress and rebaseline program costs and schedule commitments. If the Administrator notifies Congress of the need to rebaseline, NASA is required to stop funding program activities within 18 months unless Congress provides approval and additional appropriations. In our judgement, using NASA’s cost estimates from October 2019 and accounting for the removed costs from the replan, the SLS Program was required to rebaseline when the program exceeded its ABC by 33 percent at the end of FY 2019, an increase that could reach 43 percent or higher by the Artemis I launch date.    本文含有此來源中屬於公有领域的内容。
  226. ^ NASA HUMAN SPACE EXPLORATION: Persistent Delays and Cost Growth Reinforce Concerns over Management of Programs (PDF). GAO. [2020-09-15]. (原始内容存档 (PDF)于2021-10-03). NASA’s current approach for reporting cost growth misrepresents the cost performance of the program and thus undermines the usefulness of a baseline as an oversight tool. NASA’s space flight program and project management requirements state that the agency baseline commitment for a program is the basis for the agency’s commitment to the Office of Management and Budget (OMB) and the Congress based on program requirements, cost, schedule, technical content, and an agreed-to joint cost and schedule confidence level. Removing effort that amounts to more than a tenth of a program’s development cost baseline is a change in the commitment to OMB and the Congress and results in a baseline that does not reflect actual effort. [...] Further, the baseline is a key tool against which to measure the cost and schedule performance of a program. A program must be rebaselined and reauthorized by the Congress if the Administrator determines that development costs will increase by more than 30 percent. Accounting for shifted costs, our analysis indicates that NASA has reached 29.0 percent development cost growth for the SLS program. [...] In addition, as we previously reported in May 2014, NASA does not have a cost and schedule baseline for SLS beyond the first flight. As a result, NASA cannot monitor or track costs shifted beyond EM-1 against a baseline. We recommended that NASA establish cost and schedule baselines that address the life cycle of each SLS increment, as well as for any evolved Orion or ground systems capability. NASA partially concurred with the recommendation, but has not taken any action to date. [...] By not adjusting the SLS baseline to account for the reduced scope, NASA will continue to report costs against an inflated baseline, hence underreporting the extent of cost growth. NASA’s Associate Administrator and Chief Financial Officer stated that they understood our rationale for removing these costs from the EM-1 baseline and agreed that not doing so could result in underreporting of cost growth. Further, the Associate Administrator told us that the agency will be relooking at the SLS program’s schedule, baseline, and calculation of cost growth.    本文含有此來源中屬於公有领域的内容。
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引用错误:在<references>标签中name属性为“gsd-pdr-2016”的参考文献没有在文中使用

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