Engineering:National Security Space Launch

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Short description: Expendable launch system program of the United States Space Force
Delta IV Heavy liftoff from SLC-6.

National Security Space Launch (NSSL) is a program of the United States Space Force (USSF) intended to assure access to space for United States Department of Defense and other United States government payloads. The program is managed by the Assured Access to Space Directorate (SSC/AA) of the Space Force's Space Systems Command (SSC),[1] in partnership with the National Reconnaissance Office.[2]

Started in 1994 as the Evolved Expendable Launch Vehicle launch system program, the initial program goal was to make government space launches more affordable and reliable, leading to the development of the Boeing Delta IV and Lockheed Martin Atlas V EELV families. These remained the primary launch vehicles for U.S. military satellites, and were later joined by the Falcon 9 developed by SpaceX.[3][4]

On 1 March 2019, the program name was changed from EELV to National Security Space Launch (NSSL) to better reflect the growing commercial launch market and the changing nature of launch contracts, including the potential for reusable launch vehicles.[5][6]

The NSSL program launches the nation's most valuable military satellites; contracts to launch lower value payloads, such as those of the Space Test Program, are awarded using different methodologies.[7]

History

Initial program goals

The USAF began the EELV program in 1994, following many years of government-funded studies into improved systems and architecture. The intent was to replace legacy vehicles, including Delta II, Atlas II, and Titan IV. EELVs were to reduce costs by being based on standardized fairings, liquid core vehicles, upper stages, and solid rocket boosters. A Standard Payload Interface bus was also proposed as a way to save money and improve efficiency.

Reducing the cost of launches and ensuring national access to space were the two main goals of the USAF space launch/EELV program.[8] Some of the reasons why assured access to space is a priority for the United States are stated in National Presidential Directive Number 40, which reads:

Access to space through U.S. space transportation capabilities is essential to:

  1. place critical United States Government assets and capabilities into space;
  2. augment space-based capabilities in a timely manner in the event of increased operational needs or minimize disruptions due to on-orbit satellite failures, launch failures, or deliberate actions against U.S. space assets;
  3. support government and commercial human space flight.

The United States, therefore, must maintain robust, responsive, and resilient U.S. space transportation capabilities to assure access to space.[9]

Procurement of EELV boosters for military space launch was to evolve to more closely match commercial practice.[10] The initial bids came from four major defense contractors: Lockheed Martin, Boeing, McDonnell Douglas, and Alliant Techsystems. Each of the bids included a variety of concepts. Boeing initially proposed using the RS-25 Space Shuttle main engine.[11]

1990s-2000s

In October 1998 two initial launch services contracts (known as Buy 1) were awarded. Along with the award of two development agreements, the total amount was more than $3 billion.[12] Boeing was awarded a contract for 19 out of the 28 launches; Lockheed Martin was awarded a contract for the other 9. Boeing received $1.38 billion, and Lockheed Martin received $650 million for the launches.[13] Boeing and Lockheed Martin were each awarded US$500 million for the final phase of the bid. Boeing developed the Delta IV based around Common Booster Cores and the Delta Cryogenic Second Stage, while Lockheed Martin developed the Atlas V based around Common Core Boosters and the Centaur upper stage.[12]

In 2003, Boeing was found to be in possession of proprietary documents from Lockheed Martin.[14] The USAF moved 7 launches from Delta IV to Atlas V.[15] To end litigation and competition for a limited market, both companies agreed to form the United Launch Alliance (ULA) joint venture.[16] Each company has a 50% stake in ULA.[17]

2010s

Prior to 2012, the USAF was advancing another program, the Reusable Booster System and other follow-on technologies, and up to early 2012 issued contract awards for various aspects of it,[18] before the program was cancelled in October 2012.[19]

In December 2012, the DoD announced a re-opening of the EELV-class launch vehicle market to competition while authorizing the USAF to proceed with a block buy of "up to" 36 boosters from ULA. At the same time, another 14 boosters were to be procured competitively beginning in 2015, with the initial launches to be performed in 2017.[20]

The USAF signed a contract at that time with SpaceX for two launches in 2014 and 2015 to serve as proving flights to support the certification process for the Falcon 9 v1.1 and Falcon Heavy.[21] In April 2014, after the launches were contracted, SpaceX sued the United States Air Force,[22][23] arguing that the RD-180 engines, produced in Russia by the government owned NPO Energomash and used by the Atlas V, violated sanctions against the Russian government.[24] The USAF and SpaceX settled the lawsuit in Jan 2015 by opening up more launches to competitive bidding.[25][26] The USAF certified the Falcon 9 in May 2015,[27] and in 2016 SpaceX won a contract under the EELV program to launch a GPS Block III satellite payload to MEO.[28]

2018 to 2020s

The USAF began the process of competitively selecting the next generation NSSL vehicles in 2018. Announced performance requirements include:[29][30]

Orbit description Apogee (km) x perigee (km) Inclination (degrees) Mass to orbit (kg) Payload category
LEO 926 x 926 63.4 6,800 A, B
Polar 1 830 x 830 98.2 7,030 A, B
Polar 2 830 x 830 98.2 17,000 C
MEO Direct 1 18,200 x 18,200 50.0 5,330 A, B
MEO Transfer 1 20,400 x 1,000 55.0 4,080 A, B
GTO 35,786 x 190 27.0 8,165 A, B
Molniya 39,200 x 1,200 63.4 5,220 A, B
GEO 1 35,786 x 35,786 0.0 2,300 A, B
GEO 2 35,786 x 35,786 0.0 6,600 C

Category A payloads fit within a 4 m diameter payload envelope, category B payloads fit within a 5 m diameter payload envelope, and category C payloads require an extended 5 m diameter envelope.

The USAF and United States Space Force (USSF) plan to use the next generation NSSL launch vehicles until at least 2030.[31]

Launch vehicles

Since 2019 there are four vehicles certified by the Department of Defense to conduct NSSL launches: Atlas V, Delta IV Heavy, Falcon 9 and Falcon Heavy.[5] Delta IV Medium was retired in August 2019. After a two-year solicitation and competition process in 2018–2020, in August 2020 the USSF selected SpaceX (F9 and FH) and ULA's yet-to-be-certified Vulcan Centaur to supply US military launch requirements in 2022–2027.

Retired

Delta IV medium

Delta IV Medium flew with two or four SRBs on a single Common Booster Core.[32] The DCSS had 4 m diameter and 5 m diameter versions, with matching diameter payload fairings. Delta IV CBCs and DCSSs are integrated horizontally before being transported to the launchpad. The 4 m diameter DCSS was retired with the Delta IV Medium after the 22 August 2019 launch of a GPS-III satellite on a Delta IV M+(4,2) two SRBs, and a 4 m diameter DCSS and payload fairing. [33][34]

Retiring

Atlas V

Atlas V liftoff from SLC-41

Each Atlas V launch vehicle is based on a Common Core Booster powered by one NPO Energomash RD-180 engine with two combustion chambers and a Centaur upper stage powered by one or two Pratt & Whitney Rocketdyne RL10A-4-2 engines. Up to five Aerojet Rocketdyne Graphite-Epoxy Motor solid rocket boosters can be added to increase vehicle performance, and two diameters of payload fairing are available.[35]

A three-digit (XYZ) naming convention is used for the Atlas V configuration identification. An Atlas V XYZ will have a X 4.2-or-5.4-meter (14 or 18 ft) diameter payload fairing, Y solid rocket boosters (0-5), and Z RL-10's on the Centaur upper stage (1-2). As an example, an Atlas V 551 has a 5.4 m payload fairing, 5 SRBs, and 1 RL-10.[35]

In August 2021, ULA announced that Atlas V would be retired, and all 29 remaining launches had been sold.[36] (As of October 2023), seventeen launches remain. The one remaining NSSL launch is scheduled for the March 2024[37] and the remaining sixteen are allocated for non-DoD launches.

Delta IV Heavy

The Delta IV Heavy launch vehicle uses three Common Booster Cores (CBCs) each powered by a Pratt and Whitney Rocketdyne RS-68A engine, a Delta Cryogenic Second Stage 5 m (DCSS) powered by an RL10, and a 5 m payload fairing. Delta IV CBCs and DCSSs are integrated horizontally before being transported to the launchpad.[32] In 2020, ULA announced retirement of the Delta IV after 5 more launches.[38] (As of June 2023) one mission remains, in early 2024.[39]

Certified and active

Falcon 9

Falcon 9 liftoff from SLC-4E

The main features of the Falcon 9 in its Block 5 version include two stages, both powered by LOX and RP-1, with nine Merlin 1D engines on the first stage and one Merlin 1D Vacuum engine on the second stage.[40] This launcher features a reusable first stage and fairings, which lowers the cost per mission.[41]

GPS-IIIA USA-289 was the first NSSL-type B5 Falcon 9 launch. The launch occurred on December 23, 2018.[42]

Falcon Heavy

Main page: Engineering:Falcon Heavy

The Falcon Heavy is a super heavy-lift rocket developed and produced by SpaceX. It has been certified for the NSSL program after the STP-2 launch completed on 25 June 2019, as confirmed by the commander of the Air Force Space and Missile Systems Center, Lt. Gen. Thompson.[43] He clarified: "I certified them to compete last year" and "one of the requirements behind certification is to fly three missions." This requirement has been satisfied by the Falcon Heavy test flight in February 2018, Arabsat-6A in April 2019, and the STP-2 launch in June 2019. Falcon Heavy has been certified for two Phase 1A reference orbits and as of 2019, "it's not certified for all of our most stressing national security space orbits," Thompson said.[44] The USAF is working with SpaceX to mature their Falcon Heavy's design.[needs update]

As of July 2023, it has flown two classified national security flights, USSF-44 in November 2022[45] and USSF-67 in January 2023.[46]

Next generation vehicle competition

In 2018, a competitive contract award to launch national security spacecraft was conducted between United Launch Alliance (ULA), Northrop Grumman Innovation Systems (NGIS), Blue Origin, and SpaceX.

Phase 1: development of detailed designs

Two providers were to be selected to launch spacecraft to a number of reference orbits. In October 2018, the USAF awarded development funding to ULA, NGIS, and Blue Origin to further the design of their rockets before a subsequent competition for award to build the launch vehicles.[47] SpaceX received none of this funding to develop their designs, as both the Falcon 9 and Falcon Heavy had completed development and were already flying.

New Glenn

Blue Origin was awarded $500 million of phase 1 funding for further development of New Glenn as a potential competitor in future contracts.[47] As of 2019, Blue Origin expected a first launch of New Glenn in 2021. In the event, no phase 2 funding from the US government was forthcoming after August 2020 when ULA Vulcan and SpaceX were selected by the Air Force.[48] Blue Origin is considered likely to continue building and testing New Glenn, in part since they were already privately funding development prior to the Air Force NSSL competition.[49]

OmegA

Northrop Grumman was awarded US$792 million of phase 1 funding in 2018 for development of OmegA.[47] OmegA was a rocket design with two main solid stages, a cryogenic upper stage, and the possibility of additional solid-rocket strap-on boosters. As of 2019, the first flight has been stated by NGIS to be expected in 2021.[50] In the event, no phase 2 funding from the US government was forthcoming after August 2020 when ULA Vulcan and SpaceX were selected by the Air Force.[48] In 2020, Northrop Grumman announced the cancellation of OmegA.[51]

Vulcan Centaur

ULA was awarded $967 million of phase 1 funding for further development of Vulcan Centaur as a potential competitor in future contracts.[47] On 12 August 2019, ULA submitted Vulcan Centaur for phase 2 of the USAF's launch services competition. As of that time, Vulcan Centaur was on track for a 2021 launch.[52]

Phase 2: selection of two launch vendors

On 12 August 2019, at least three of the four companies submitted their final bids for the launch services competition. SpaceX bid the existing Falcon 9 and Falcon Heavy, while Blue Origin was expected to bid New Glenn, ULA bid Vulcan Centaur, and NGIS's bid status was not reported. Blue Origin also filed a pre-award protest of the request for proposal arguing that the requirements were ambiguous.[53][needs update]

The United States Department of the Air Force announced the results of the approximately US$3.5 billion National Security Space Launch Phase 2 Launch Service Procurement on 7 August 2020. SpaceX and ULA were the two vendors selected via the competition to supply launches to the US military in the 2022–2026 timeframe.[49][48] The US Space Force (USSF) plans 30–34 launches during these five fiscal years. ULA is expected to handle 60 percent of the launches while SpaceX will handle 40 percent of the launches over the five-year period.[48][49]

The contract type for the phase 2 contracts is new for NSSL launches as it will be a "firm-fixed-price, indefinite-delivery" type of launch contract.[54] The awards in August 2020 are a major part of "the transition of the national security launch program to take advantage of commercial innovation and private investments in launch vehicles."[48]

NSSL Phase 3

In 2023, USSF released a draft RFP for "Phase 3" of NSSL, which covers the five fiscal years 2025-2029. Unlike the earlier NSSL contracts, Phase 3 is divided into two "lanes". Lane 1 covers less demanding missions and is structured to encourage new launch providers. Lane 2 is more similar to Phase 2 and requires each provider to be able to handle all NSSL requirements. However, Lane 2 allows for up to three providers instead of just the two providers of Phase 2.[55] Proposals were due December 15, 2023 and awards are expected in mid to late 2024.[56]

Missions

Name Launch Vehicle Award Date
Year Phase
NROL-52 Atlas V 421 2016 Buy 1 15 October 2017
NROL-71 Delta IV Heavy 2016 Buy 1 19 January 2019
GPS III-2 Delta IV M+ 2016 22 August 2019
GPS III-1 Falcon 9 2016 1A 23 December 2018
AEHF-5 Atlas V 551 2016 8 August 2019
WGS-10 Delta IV M+ 2016 15 March 2019
GPS III-3 Falcon 9 2017 1A 30 June 2020
USSF-8 Atlas V 511 2018 1A 21 January 2022
USSF-12 Atlas V 541 2018 1A 1 July 2022
GPS III-4 Falcon 9 2018 1A 5 November 2020
GPS III-5 Falcon 9 2018 1A 17 June 2021
GPS III-6 Falcon 9 2018 1A 18 January 2023
USSF-52 Falcon Heavy 2018 1A 29 December 2023
SBIRS GEO-5 Atlas V 421 2019 1A 18 May 2021
SBIRS GEO-6 Atlas V 421 2019 1A 4 August 2022
NROL-107 Atlas V 551 2019 1A 10 September 2023
NROL-68 Delta IV Heavy 2019 1 21 June 2023
NROL-91 Delta IV Heavy 2019 1 24 September 2022
NROL-44 Delta IV Heavy 2019 1 10 December 2020
NROL-82 Delta IV Heavy 2019 1 26 April 2021
NROL-70 Delta IV Heavy 2019 1 March 2024
NROL-101 Atlas V 531 2019 1 13 November 2020
AEHF-6 Atlas V 551 2019 1 26 March 2020
USSF-7 Atlas V 501 2019 1 17 May 2020
USSF-44 Falcon Heavy 2019 1A 1 November 2022
NROL-87 Falcon 9 2019 1A 2 February 2022
NROL-85 Falcon 9 2019 1A 17 April 2022
USSF-51 Atlas V 2020 2[57] March 2024
USSF-106 Vulcan Centaur 2020 2[57] 2024
USSF-67 Falcon Heavy 2020 2[57] 15 January 2023
USSF-112 Vulcan VC4 2021 2[58] 2024
USSF-87 Vulcan VC4 2021 2[58] 2024
USSF-36 Falcon 9 2021 2[58] H2 2024
NROL-69 Falcon 9 2021 2[58] H1 2024
GPS III-7 Vulcan Centaur 2022 2[59] June 2024
USSF-16 Vulcan Centaur 2022 2[59]
USSF-23 Vulcan Centaur 2022 2[59]
USSF-43 Vulcan Centaur 2022 2[59]
WGS-11+ Vulcan Centaur 2022 2[59]
USSF-124 Falcon 9 2022 2[59] March 2024
USSF-62 Falcon 9 2022 2[59] 2024
SDA T1TL-A Falcon 9 2022 2[59] 2024
NROL-64 Vulcan Centaur 2023 2[60] 2025
NROL-83 Vulcan Centaur 2023 2[60] 2025
GPS III-8 Vulcan Centaur 2023 2[60] February 2025
USSF-114 Vulcan Centaur 2023 2[60] 2025
SDA T1TR-B Vulcan Centaur 2023 2[60] 2025
SDA T1TR-D Vulcan Centaur 2023 2[60] 2025
USSF-31 Falcon 9 2023 2[60] 2024
SDA T1TL-B Falcon 9 2023 2[60] September 2024
SDA T1TL-C Falcon 9 2023 2[60] October 2024
SDA T1TL-D Falcon 9 2023 2[60] November 2024
SDA T1TL-E Falcon 9 2023 2[60] December 2024
SDA T1TL-F Falcon 9 2023 2[60]
GPS III-9 Vulcan Centaur[61] 2023 2[62] 2025
NROL-73 Vulcan Centaur[61] 2023 2[62]
NROL-56 Vulcan Centaur[61] 2023 2[62]
STP-5 Vulcan Centaur[61] 2023 2[62]
SILENTBARKER 2/NROL-118 Vulcan Centaur[61] 2023 2[62]
USSF-57 Vulcan Centaur[61] 2023 2[62]
NROL-100 Vulcan Centaur[61] 2023 2[62]
USSF-95 Vulcan Centaur[61] 2023 2[62]
NROL-109 Vulcan Centaur[61] 2023 2[62]
SDA T2TL-B Vulcan Centaur[61] 2023 2[62]
USSF-25 Vulcan Centaur[61] 2023 2[62]
SDA T1TR-C Falcon 9[61] 2023 2[62] Q4 2024
SDA T1TR-A Falcon 9[61] 2023 2[62]
NROL-77 Falcon 9[61] 2023 2[62]
SDA T1TR-E Falcon 9[61] 2023 2[62]
GPS III-10 Falcon 9[61] 2023 2[62]
USSF-75 Falcon Heavy[61] 2023 2[62]
SDA T2TL-A Falcon 9[61] 2023 2[62]
SDA T2TL-C Falcon 9[61] 2023 2[62]
USSF-70 Falcon Heavy[61] 2023 2[62]
GPS IIIF-1 Falcon Heavy[61] 2023 2[62]

References

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  2. ↑ Tadjdeh, Yasmin (July 20, 2021). "JUST IN: National Reconnaissance Office Embracing Commercial Tech". National Defense Magazine. https://www.nationaldefensemagazine.org/articles/2021/7/20/national-reconnaissance-office-embracing-commercial-tech. 
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  21. ↑ "SpaceX Awarded Two EELV-Class Missions from the United States Air Force". December 5, 2012. https://www.spacex.com/press/2012/12/19/spacex-awarded-two-eelv-class-missions-united-states-air-force. 
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  25. ↑ Gallagher, Sean (January 25, 2015). "SpaceX elbows into Air Force launch program after dropping lawsuit". Ars Technica. https://arstechnica.com/business/2015/01/spacex-elbows-into-air-force-launch-program-after-dropping-lawsuit/. 
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  27. ↑ Gruss, Mike (May 26, 2015). "SpaceX Falcon 9 Certified for Military Launches". SpaceNews. https://spacenews.com/u-s-air-force-certifies-falcon-9-for-military-launches-2/. 
  28. ↑ Gruss, Mike (April 27, 2016). "SpaceX wins $82 million contract for 2018 Falcon 9 launch of GPS 3 satellite". SpaceNews. http://spacenews.com/spacex-wins-82-million-contract-for-2018-falcon-9-launch-of-gps-3-satellite/. 
  29. ↑ Space and Missile Systems (5 Oct 2018). "EELV LSA RFP OTA". https://www.fbo.gov/utils/view?id=e2c583b4a02911ba7f59eff384b38664. "table 10 of page 27" 
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  31. ↑ "DOD Releases Fiscal Year 2021 Budget Proposal" (in en-US). https://www.defense.gov/Newsroom/Releases/Release/Article/2079489/dod-releases-fiscal-year-2021-budget-proposal/. 
  32. ↑ 32.0 32.1 Graham, William (April 3, 2012). "ULA Delta IV launches the NROL-25 military satellite from VAFB". NASASpaceFlight.com. http://www.nasaspaceflight.com/2012/04/live-ula-delta-iv-launch-nrol-25-military-satellite-vafb/. 
  33. ↑ "United Launch Alliance Successfully Launches GPS III Satellite for U.S. Air Force Space and Missile Systems Center". https://www.ulalaunch.com/about/news/2019/08/22/united-launch-alliance-successfully-launches-gps-iii-satellite-for-u.s.-air-force-space-and-missile-systems-center. 
  34. ↑ "Delta IV Medium's well-earned retirement with GPS finale" (in en-US). 2019-08-22. https://www.nasaspaceflight.com/2019/08/delta-iv-medium-retirement-gps-finale/. 
  35. ↑ 35.0 35.1 "Atlas V". ULA. 2010. pp. 1–4. http://www.ulalaunch.com/site/docs/product_cards/guides/AtlasVUsersGuide2010.pdf. 
  36. ↑ Roulette, Joey (26 August 2021). "ULA stops selling its centerpiece Atlas V, setting path for the rocket's retirement". The Verge. https://www.theverge.com/2021/8/26/22641048/ula-boeing-lockheed-end-sales-atlas-v-rocket-russia-rd180. 
  37. ↑ "Atlas V - USSF-51". Next Spaceflight. 8 October 2023. https://nextspaceflight.com/launches/details/5055. 
  38. ↑ "ULA targeting September 26 for next Delta 4-Heavy launch attempt". Spaceflight Now. 17 September 2020. https://spaceflightnow.com/2020/09/17/ula-targeting-sept-26-for-next-delta-4-heavy-launch-attempt/. 
  39. ↑ Clark, Stephen (June 22, 2023). "Delta 4-Heavy rocket lifts off with NRO spy satellite". Spaceflightnow. https://spaceflightnow.com/2023/06/22/delta-4-heavy-nrol-68-coverage/. 
  40. ↑ "Falcon 9 & Falcon Heavy". https://spacex-info.com/falcon-9-falcon-heavy/. Retrieved 19 October 2021. 
  41. ↑ "SpaceX flies historic 10th mission of a Falcon 9 as Starlink constellation expands". May 8, 2021. https://www.nasaspaceflight.com/2021/05/historic-10th-falcon9-reflight/. 
  42. ↑ Clark, Stephen (December 17, 2018). "Air Force requirements will keep SpaceX from landing Falcon 9 booster after GPS launch". Spaceflight Now. https://spaceflightnow.com/2018/12/17/air-force-requirements-will-keep-spacex-from-recovering-falcon-9-booster-after-gps-launch/. 
  43. ↑ Erwin, Sandra (September 21, 2019). "Air Force certified Falcon Heavy for national security launch, but more work needed to meet required orbits". https://spacenews.com/air-force-certified-falcon-heavy-for-national-security-launch-but-more-work-needed-to-meet-required-orbits/. 
  44. ↑ Erwin, Sandra (September 21, 2019). "Air Force certified Falcon Heavy for national security launch but more work needed to meet required orbits". https://spacenews.com/air-force-certified-falcon-heavy-for-national-security-launch-but-more-work-needed-to-meet-required-orbits/. 
  45. ↑ "USSF-44: Space Force successfully completes first mission on Falcon Heavy rocket". 12 December 2022. https://aerospace.org/article/ussf-44-space-force-successfully-completes-first-mission-falcon-heavy-rocket. 
  46. ↑ "SpaceX Falcon Heavy launches USSF-67 from 39A". NASASpaceFlight.com. 15 January 2015. https://www.nasaspaceflight.com/2023/01/ussf-67-launch/. 
  47. ↑ 47.0 47.1 47.2 47.3 Sandra Erwin (10 October 2018). "Air Force Awards Launch Vehicle Development Contracts to Blue Origin Northrop Grummand ULA". Space News. https://spacenews.com/air-force-awards-launch-vehicle-development-contracts-to-blue-origin-northrop-grumman-ula/. 
  48. ↑ 48.0 48.1 48.2 48.3 48.4 Erwin, Sandra (7 August 2020). "Pentagon picks SpaceX and ULA to remain its primary launch providers". SpaceNews. https://spacenews.com/pentagon-picks-spacex-and-ula-to-launch-national-security-satellites-for-next-five-years/. 
  49. ↑ 49.0 49.1 49.2 Berger, Eric (7 August 2020). "In a consequential decision, Air Force picks its rockets for mid-2020s launches". Ars Technica. https://arstechnica.com/science/2020/08/the-air-force-selects-ula-and-spacex-for-mid-2020s-launches/. 
  50. ↑ "OmegA". https://www.northropgrumman.com/MediaResources/MediaKits/OmegARocket/pdf/OmegA_Factsheet.pdf. 
  51. ↑ "Northrop Grumman to terminate OmegA rocket program" (in en-US). 2020-09-09. https://spacenews.com/northrop-grumman-to-terminate-omega-rocket-program/. 
  52. ↑ "Vulcan Centaur Rocket on Schedule for First Flight in 2021: ULA Submits Proposal for U.S. Air Force's Launch Services Competition". ULA. 12 August 2019. https://www.ulalaunch.com/about/news/2019/08/12/vulcan-centaur-rocket-on-schedule-for-first-flight-in-2021. 
  53. ↑ Emre Kelly (12 August 2019). "Blue Origin files protest challenging 'flawed' Air Force strategy for choosing launches". FloridaToday. https://www.floridatoday.com/story/tech/science/space/2019/08/12/blue-origin-files-protest-challenging-flawed-air-force-strategy-for-choosing-launches-ula-spacex/1986706001/. 
  54. ↑ "Contracts for August 7, 2020". https://www.defense.gov/News/Contracts/Contract/Article/2305454/. 
  55. ↑ Lentz, Danny; Davenport, Justin (July 22, 2023). ""Space Force releases NSSL phase three second draft"". https://www.nasaspaceflight.com/2023/07/nssl-phase-three-update. 
  56. ↑ Erwin, Sandra (October 5, 2023). ""Space Force releases final call for bids for national security launch services"". https://spacenews.com/space-force-releases-final-call-for-bids-for-national-security-launch-services/. 
  57. ↑ 57.0 57.1 57.2 "FY20 NSS Missions". U.S. Air Force. August 7, 2020. https://www.af.mil/News/Article-Display/Article/2305576/space-force-awards-national-security-space-launch-phase-2-launch-service-contra/. 
  58. ↑ 58.0 58.1 58.2 58.3 "FY21 NSS Missions". U.S. Department of Defense. https://www.defense.gov/News/Contracts/Contract/Article/2530911/source/GovDelivery/. 
  59. ↑ 59.0 59.1 59.2 59.3 59.4 59.5 59.6 59.7 "FY22 NSS Missions". Space Systems Command. https://www.ssc.spaceforce.mil/Portals/3/Documents/PRESS%20RELEASES/SSC%20Issues%20Launch%20Task%20Orders%20for%20FY22%20NSS%20Missions.pdf?ver=eR_TvXz3KYJArhCmiTk9TA%3D%3D. 
  60. ↑ 60.00 60.01 60.02 60.03 60.04 60.05 60.06 60.07 60.08 60.09 60.10 60.11 "FY23 NSS Missions". Space Systems Command. https://www.ssc.spaceforce.mil/Portals/3/Documents/PRESS%20RELEASES/Space%20Systems%20Command%20assigns%20missions%20for%20National%20Security%20Space%20Launch%20Phase%202%20FY23%20Order%20Year.pdf?ver=jwJkHKLFFtsxR635uXxxkw%3D%3D. 
  61. ↑ 61.00 61.01 61.02 61.03 61.04 61.05 61.06 61.07 61.08 61.09 61.10 61.11 61.12 61.13 61.14 61.15 61.16 61.17 61.18 61.19 61.20 "After Vulcan slips, Space Force ends up awarding more missions to SpaceX". Ars Technica. https://arstechnica.com/space/2023/11/after-vulcan-slips-space-force-ends-up-awarding-more-missions-to-spacex/. 
  62. ↑ 62.00 62.01 62.02 62.03 62.04 62.05 62.06 62.07 62.08 62.09 62.10 62.11 62.12 62.13 62.14 62.15 62.16 62.17 62.18 62.19 62.20 "Space Systems Command announces 21 mission assignments for National Security Space Launch Phase 2 Procurement". Space Systems Command. https://www.ssc.spaceforce.mil/Portals/3/Documents/PRESS%20RELEASES/Space%20Systems%20Command%20announces%2021%20mission%20assignments%20for%20National%20Security%20Space%20Launch%20Phase%202%20Procurement.pdf. 



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