DIRECT issue rebuttal over NASA analysis of Jupiter launch vehicle
The team behind the alternative exploration architecture known as DIRECT have released a rebuttal document, countering claims made by NASA’s Constellation Program, ahead of the Blue Ribbon review for human space flight. The document specifically targets a series of claims made by a NASA team in May and October of 2007, which found the Jupiter launch vehicle to be unable to achieve claimed performance targets.
History of DIRECT:
DIRECT is an alternative architecture, proposed to replace Ares I and Ares V with a single “Jupiter” vehicle, capable of performing both roles.
The DIRECT approach claims to offer significant improvements in performance, schedule, and budget expenditure – when compared to Ares – by relying more on the existing technology and components of the space shuttle and EELV programs.
The DIRECT proposal has its roots in the Marshall Space Flight Center (MSFC) studies (1990s) to design a shuttle-based heavy lift cargo vehicle to compliment the space shuttle. Known as the National Launch System (NLS), the concept was deemed to have significant merit – before being deleted due to budgetary concerns.
In 2006, a group of engineers and members of the space community revived and modernized the concept, calling it DIRECT.
The proposal was first presented in October 2006, followed by a major revision in September 2007, known as DIRECT 2.0. The team claims to be comprised of eight public representatives and 62 NASA and contractor engineers – who work on the project on their own time.
NASA Analysis Background:
As DIRECT gained attention via two AIAA papers, and presentations at the ISDC, before MSFC performed two reviews of the DIRECT 2.0 architecture in May and October of 2007 – which found serious issues with DIRECT’s performance and capabilities.
“Analysis of the DIRECT architecture shows significant performance shortfall in assessed capability,” noted the October, 07 analysis.
“The DIRECT architecture aggressively estimates its stage dry mass predictions, which results in optimistic in-space performance. Consequently, the Direct 2.0 would likely be a Three Vehicle Launch Solution Mission to accomplish the Project Constellation Payload Requirements with NASA design margins, ground rules and assumptions.
“Assessed performance has improved from May 2007 EOR-LOR, but still fails to meet minimum requirements by at least 50 percent of needed Lander Payload.”
In order to back up these claims, NASA commissioned a ‘Team B’ review to attempt to design and fly a DIRECT lunar mission using NASA tools and specifications. Their results showed significantly larger masses and lower performance predictions, than those claimed by DIRECT.
“DIRECT currently unsuitable for its proposed goal of replacing the Ares I/V architecture to carry out the earth-to-TLI transportation functions for the Constellation Programs,” noted the review.
The analysis also attacks the infrastructure and development of the DIRECT vehicles, specifically DIRECT’s claimed redesign of the External Tank vs. Ares I’s clean sheet upper stage.
“Assessment of design would lead to major redesign, development and qualification of Mod ET Core for Jupiter 232 missions. Predicted touch labor of Ares 1 Upper Stage estimated to be significantly less than current ET touch labor.
“Examined approaches like this in the past 20 years: Concluded that this effort incurs significant expense and development with marginally applicable STS ET heritage.
“The Jupiter common core requires a new: Main Propulsion System, thrust structure, avionics, forward LOX tank structure and a payload shroud, substantial intertank/LH2 modifications, and a stack integration effort.
The October 07 analysis’ final major criticism of DIRECT referenced Ares’ operational safety and simplicity.
“DIRECT launch architecture requires increased number of spacecraft separations and dockings for all phases, increasing risk Separation, flip around and docking of Orion to Altair Rendezvous and docking of Orion-Altair stack to first EDS pre-TLI burn. DIRECT shows a 1/1400 PLOC for Jupiter 232 Lunar/Mission.
DIRECT’s response to NASA’s analysis is forthcoming via a 100+ page rebuttal document that deals with the claims and explains why the criticisms are flawed – according to DIRECT. *CLICK HERE TO DOWNLOAD THE PRESENTATION*
The document centers around the allegation that DIRECT was significantly misinterpreted by NASA’s analysis teams in an attempt to discredit the proposal.
“NASA’s October 2007 analysis of DIRECT, on the surface, appears to be a carefully executed analysis of the DIRECT architecture and its central launch vehicle, Jupiter,” notes the rebuttal document.
“However, a closer examination of the document reveals significant flaws in the evaluation of DIRECT that sets up a scenario where DIRECT would inevitably look inferior when compared to Ares.
“The errors are so numerous that the only conclusion possible is that this document was not a true analysis, but rather an attempt to discredit the DIRECT architecture.”
DIRECT claims that NASA’s inability to match the DIRECT team’s claimed performance hinges on the arbitrary mass increase of the EDS (Earth Departure Stage) by ‘Team B’.
“For Every 1 kg Upper Stage Growth, 3 kg Less Payload Delivered through TLI. Arbitrarily increasing the mass of the Upper Stage penalizes the performance of the entire system 3-fold.
“On pages 55 & 56 of NASA’s Analysis, a breakdown of the mass of the Upper Stage shows NASA’s ‘Case #2 – Team B’ design methodology using INTROS, results in a 17,797kg difference in burnout mass for the Upper Stage; 23,062 kg vs. 40,859 kg – a 77 percent performance penalty.
“A penalty applied to the Upper Stage mass of nearly 18mT results in a net reduction of EDS lunar performance by nearly 36mT.”
DIRECT contends that this mass increase is due to the use of a NASA design tool that does not assume the Centaur-based components of DIRECT’s upper stage.
“NASA’s Upper Stage was designed using the NASA-developed “INTROS” tool,” claims the rebuttal. “While this is based on heritage data, this tool has never been utilized in the production of any flying vehicle to date. Boeing did not utilize the tool for its Delta-IV and Lockheed Martin did not utilize the tool for the Atlas V – the two most modern US launchers.
“NASA’s analysis (also) ignores DIRECT’s plan to use a Common Bulkhead design for the Jupiter Upper Stage.”
The DIRECT team also attempt to back up their claims that the External Tank (ET) would only have to undergo minor redesign – which is an area of contention due to claims DIRECT ignore the testing requirements any changes to the ETs require – by noting the “minor” claim is comparative to the “major” changes required by Ares I and Ares V.
“It is worth noting that the requirement to build two new SRB designs, a vast new 10m Core Stage, two new Upper Stages and two completely separate production and launch processing infrastructures to support both Ares I – and then Ares V – would certainly qualify as a “major” undertaking,” DIRECT claim – adding they would also save billions in development costs.
“In that single context, it might be accurate to describe DIRECT’s plans as comparatively ‘minor’.
“Development costs for Jupiter-120 are approximately $5,000m lower than Ares I. Development costs for Jupiter-232 are a further $9,000m lower than Ares V. Operations costs for two very different Ares vehicles are approx. $3,100m higher per year than for the common-core Jupiter’s. Total DIRECT lifecycle savings thru 2020 are greater than $19,000m.”
To address NASA’s last major criticism concerning safety and operations, DIRECT points out that the risk calculations have been easily skewed, and are essentially subjective.
“There is a ‘time factor’ at work also which severely skews NASA’s conjecture. The Jupiter’s LOC (Loss Of Crew) and LOM (Loss Of Mission) figures were calculated in late October 2007,” DIRECT claim. “This date coincides with the Ares I Integrated System Technical Interchange Meeting (IS-TIM) on November 8.
“The design of Ares I has not changed significantly since that time, only the methodology for calculating the risk has altered since then. Somehow Ares I has doubled its LOC claims to “1/2400″ – according to NASA, yet the Ares I still uses all the same engines and stages.”
However, it appears DIRECT completely ignore the central claim by Constellation that their first stage SRB has obvious safety benefits when compared to Jupiter’s “numerous moving parts” in its first stage liquid engines. DIRECT also admit they are still awaiting new analysis.
“At time of writing, DIRECT is still awaiting results of a new analysis and expects similar improvements as Ares,” the rebuttal admits.
DIRECT claim that they would have lower total mission risk due to its capability to return safety systems that have been stripped of Orion due to mass issues.
“Because of DIRECT’s surplus performance, all of the capabilities deleted from Orion in the Zero Base Vehicle (ZBV) studies could be added back in,” they claim.
“If those systems can be reintegrated, it would dramatically improve the overall mission LOM figures, which represent a far larger portion of the total risks than just the launch.”
DIRECT anticipates being heavily involved in the upcoming Blue Ribbon review for human space flight – which will include an evaluation on NASA’s current exploration direction - and the team will be presenting their latest proposals at the Orlando ISDC conference at the end of May and will also have representatives there able to discuss the latest evolutions of the proposal.