DIRECT
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| DIRECT | |
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| Fact sheet | |
|---|---|
| Function | Partially re-usable launch vehicle |
| Manufacturer | None |
| Country of origin | United States |
| Size | |
| Height | 85 to 95m |
| Diameter | 8.41 m (identical to Shuttle External Tank) (27ft 7in) |
| Mass | 2,027,890 to 2,371,593 kg |
| Stages | 2 or 3 |
| Capacity | |
| Payload to LEO | 46,635 to 105,895 kg (102,812 to 233,458 lb) |
| Launch History | |
| Status | Proposal |
| Launch sites | LC-39, Kennedy Space Center |
| Notable payloads | Orion EDS LSAM |
| Boosters (Stage 0) - Shuttle SRB | |
| No boosters | 2 |
| Engines | 1 solid |
| Thrust | 14,820 kN (3,331,400 lbf) |
| Specific impulse | 267.5 sec |
| Burn time | 124 seconds |
| Fuel | solid |
| First Stage (Jupiter-120 Variant) - Core Stage based on Shuttle External Tank |
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| Engines | (2 RS-68 "Ablative") |
| Thrust | 6,681 kN (1,502,000 lbf) |
| Specific impulse | 409 sec |
| Burn time | 442 sec |
| Fuel | LOX/LH2 |
| First Stage (Jupiter-232 Variant) - Core Stage based on Shuttle External Tank |
|
| Engines | (3 RS-68 "Ablative") |
| Thrust | 10,022 kN (2,253,000 lbf) |
| Specific impulse | 409 sec |
| Burn time | 294 sec |
| Fuel | LOX/LH2 |
| Second Stage (Jupiter-232 Variant) - J-232 EDS | |
| Engines | 2 J-2XD |
| Thrust | 2,433 kN (547,000 lbf) |
| Specific impulse | 448 sec |
| Burn time | 435 sec |
| Fuel | LOX/LH2 |
DIRECT is a proposal for a set of Shuttle Derived Launch Vehicles to be used for future spaceflights. Developed independently from NASA, DIRECT proposes an alternative system of launch vehicles for the U.S. government's Vision for Space Exploration, which would replace those NASA is currently developing in its Project Constellation. Like Project Constellation, however, DIRECT would enable the missions to the Moon, Mars and beyond that were outlined in the Vision for Space Exploration. The name "DIRECT" is intended to emphasize the use of components with a more direct heritage to the existing Space Shuttle design.
Contents |
[edit] Safer, Simpler, Sooner
The proposal would replace the planned Ares I and Ares V with two launch vehicles developed more directly from existing Shuttle components. Proponents assert that DIRECT would cut development and manufacturing costs and advance program schedules, in part by minimizing the modification of existing Shuttle components, and also by creating greater commonality between the crewed and unpiloted launch vehicles to be used in the program.
[edit] Origins
The basic concept behind DIRECT was first proposed in 1986 by NASA's Marshall Space Flight Center in the aftermath of the Space Shuttle Challenger disaster. It was promoted as one of the most logical alternatives for launching unmanned cargo and even potentially a re-started Apollo spacecraft program if required. There were, however, no funds available to NASA for building any new vehicles, so the idea was shelved and NASA concentrated on fixing and operating the Space Shuttle program instead.
In 1991 the National Launch System brought the idea back to life. Proposed by NASA and the DoD as an alternative to the Titan IV. The design was based on the same SRB's as Shuttle, the same core tanking, but it had four smaller, inexpensive engines and considerably lower performance than the original concept.
Then in 2005, NASA's Exploration Systems Architecture Study (ESAS) included a very similar design, but with three of the Space Shuttle Main Engines (SSME). Known as LV-24 in Crew launch form, and LV-25 in Cargo configuration, the idea was dismissed because it did not have sufficient performance for the proposed lunar program - however the concept was not considered using an EDS.
According to its proponents, DIRECT v1.0 was the product of a three-month grass-roots study produced by nearly 50 NASA engineers and managers working purely in their free time, and a small group of dedicated enthusiasts. DIRECT takes the final ESAS recommendation of using the EDS during the ascent phase of the flight to gain additional launch performance on the Cargo LV, and applies this same methodology to the basic LV 24/25 design - at which point LV-24/25 considerably out-performs the ESAS's final solutions for Lunar missions.
The next change in DIRECT's development was in response to NASA dropping the SSME on their Cargo LV design. This was due to the high manufacturing cost of the SSME engines, and the difficulty in producing the required number of units per year with existing manufacturing facilities. So NASA chose to replace them with five RS-68 engines to make the Ares V Cargo LV. This same change was also applied to DIRECT's concept. Analysis showed, however, that the number of engines required for this particular vehicle could be reduced to just two of the basic RS-68 engines. Additional performance and IMLEO could be provided by upgrading the main engines with the Regenerative Cooling Nozzles to improve their efficiency. It should be noted, however, that the analysis also demonstrated that this improvement, while desirable, is not required in order to accomplish the basic missions of both the crew and cargo programs.
The proposal was submitted on October 25, 2006 to NASA's Administrator, Michael D. Griffin, and a wide range of industry, political and advocacy groups involved in the current development plans. v2.0 of the proposal is a 9 month refinement study which was announced on September 19th 2007 at the AIAA "Space 2007" Conference in Long Beach, CA.
[edit] Advantages and disadvantages
Proponents of DIRECT also argue that this proposal will enable NASA to fulfill the mandate of the Vision for Space Exploration faster, safer, and sooner than the planned Ares I and Ares V, at a much lower cost and with far less programmatic risk. Unlike the budget plans for Ares I and Ares V, DIRECT will still allow NASA sufficient room in its current budgets beyond launch vehicle development and operations to continue funding other missions such as the International Space Station beyond 2016, while being better able to withstand the unpredictability of future annual congressional/administration budget allocations.
The DIRECT proposal calls for NASA to use the massive development-cost and fixed-cost savings from DIRECT to accelerate the VSE's schedule for returning to the moon, to continue to fly missions to support the International Space Station, and to potentially fly other missions such as servicing missions to the Hubble Space Telescope. Like NASA's official Constellation plans, the DIRECT proposal calls for ensuring that the existing NASA Space Shuttle industrial base and workforce at sites around the U.S. would be retained (which is important from both the standpoint of maintaining Congressional support and maintaining the skills and know-how of this workforce). However, compared to Constellation, the much shorter gap in manned U.S. space flight under DIRECT would prevent the type of knowledge-loss that NASA suffered in the gap between Apollo and the Shuttle in the late 1970's and the related localized economic hardship in Florida's Space Coast that was seen during the same time period.
Opponents of DIRECT argue that the safety factor of this proposal is not as good as that of the original ESAS Crew LV proposal. DIRECT's proponents counter that the Jupiter 120 Crew LV has much greater safety margins than NASA's current plans for an Ares I Crew LV, which is a significantly different vehicle from the originally selected ESAS Crew LV. Opponents also contend that, as a plan developed outside of official NASA channels (NIH), DIRECT stands little chance of being implemented.
[edit] Design
The DIRECT launch vehicle concept consists of a core stage, based on many existing elements of the current External Tank with either two or three Pratt & Whitney/Rocketdyne RS-68 main engines mounted directly underneath, and a pair of Alliant Techsystems 4-segment Solid Rocket Boosters (SRBs) unchanged from the Space Shuttle today. According to its proponents, initial performance to Low Earth Orbit (LEO) [specifically to 42x120nm, 28.5-degree inclination initial orbit] for this initial variant of the DIRECT Crew LV is conservatively expected to be at least 46,635kg (102,812lb), which is 250% of Ares I's 19,300kg (42,500lb) maximum performance. This means that an Orion spacecraft could be launched on top of the vehicle, along with 24,600kg (54,000lb) of additional cargo on every flight - a useful capability that is impossible with the Ares I.
An optional upper stage, known as the Earth Departure Stage (EDS), powered by two Pratt & Whitney/Rocketdyne J-2XD engines would be used to increase payload capacity for certain missions. Payload performance to LEO increases to at least 103,342kg (227,829lb).
Gross performance for the two Ares I and Ares V launchers required for every Lunar mission is expected to be no more than 150,900kg (333,000lb). By comparison, two DIRECT J-232 vehicle, one launching Crew and spacecraft and the other launching mostly propellant, are capable of launching in excess of 220,000kg (485,000lb), including greater performance margin reserves.
To speed development of DIRECT, the RS-68 engines on the core stage would be man-rated versions of those used successfully on the current Delta IV program. DIRECT explicitly plans not to require performance upgrades, even rejecting the 6% additional performance NASA requires from the RS-68 for use on the Ares V instead opting to operate the engines at the lower performance levels being used today to gain the maximum possible reliability and safety.
Unlike NASA's Ares I, DIRECT does not require any new engines to be developed for the first vehicle, designated J-120, in order to fly the first manned Orion spacecraft. This removes the greatest cost and schedule impacts that Ares I faces. J-2XD engines are only required by DIRECT on the optional upper stage for the later lunar missions. Even then DIRECT would only require the lower-thrust, lest-costly J-2X "Development" variant. DIRECT does not require the additional performance of the fully upgraded J-2X engine needed by both Ares I and Ares V.
Similarly, DIRECT does not require the very expensive development of new 5-segment Solid Rocket Boosters as needed by Ares I and Ares V. The existing fully man-rated 4-segment Shuttle SRB's provide adequate thrust for DIRECT while helping to reduce costs.
Finally, DIRECT's Core Stage uses the existing 8.41m diameter of the Shuttle's External Tank. Unlike Ares V with its 10.06m diameter Core Stage, this allows DIRECT to re-use the existing manufacturing tooling for the External Tank at the Michoud Assembly Facility, the existing Pegasus barge used to transport the tank from Michoud to Kennedy Space Center, the existing work platforms in the Vehicle Assembly Building, the existing Mobile Launcher Platforms and Crawler-Transporters, and much of the structure of the existing Fixed Service Structure and Flame Trenches at Launch Complex 39.
While DIRECT does not require any of the upgraded hardware needed by the Ares launchers, should additional performance be required in the future DIRECT can take advantage of these enhancements to increase performance - but they are not requirements in the critical path to success and the additional capital investment is not required.
[edit] Integrated Approach
Once the basic vehicle was pinned down, more NASA engineers and managers started to support the concept and offer their time to flesh out the concept from a wider perspective. These professionals contributed to creating a complete cost analysis comparison, a detailed series of evaluations for supporting facilities such as data on the existing manufacturing facilities for the External Tank at the Michoud Assembly Facility and the various launch-processing facilities currently at the Kennedy Space Center.
From these contributions, a clear difference in cost, schedule, maintenance, manufacturing & launch processing flow became apparent between the Ares and DIRECT approaches. DIRECT would re-use almost all of the existing facilities, whereas Ares I and Ares V each required seriously overhauled or completely replaced facilities – and each required its own set. This impacts almost every aspect of the operation from cost to design, development, testing, evaluation, implementation, schedule, risk mitigation, workforce retention and safety.
A fully integrated assessment of all these factors, under the outlines of the political requirements NASA must operate within, and a detailed analysis of the wider range of Lunar mission procedures which DIRECT can offer, resulted in the complete DIRECT Launch Vehicle Proposal.
[edit] Criticism and Changes
The original DIRECT 1.0 proposal created a wave of discussion within both professional NASA/aerospace circles and within the broader community of NASA supporters and enthusiasts. Approximately 2000 posts about DIRECT 1.0 appeared on the public forum at NASASpaceflight.com over a 7 month period.
In late 2006, NASA's Dr. Doug Stanley declared that the DIRECT 1.0 proposal could not work as it relied on overly-optimistic and speculative performance specifications for an upgraded RS-68 Regen engine. Dr. Stanley produced official specifications from Pratt & Whitney/Rocketdyne about the RS-68 Regen upgrades to prove his point. Later evidence from PWR concluded that DIRECT 1.0's overly-optimistic RS-68 variant was in fact technically possible, although was going to be expensive and time-consuming to develop.
[edit] DIRECT 2.0
On May 10, 2007, a revised DIRECT 2.0 proposal was released by the same volunteer group to meet peer-reviewed critiques of the initial proposal. After several months of work, the team came back with a revised proposal, DIRECT 2.0. To address criticism of relying on engine studies rather than working engines, DIRECT 2.0 uses only man-rated versions of the existing RS-68 with no performance upgrades at all and the lower of two specifications of J-2X engine which Pratt & Whitney/Rocketdyne are currently developing for NASA's Ares launchers. DIRECT 2.0 introduced a scalable, modular family of Shuttle-derived launch vehicles, starting with the DIRECT Jupiter-120 and DIRECT Jupiter-232.
The Jupiter 232 heavy launch vehicle in the revised DIRECT 2.0 proposal differs from the original proposal primarily by specifying the use of two existing J-2 engines on the Earth Departure Stage (EDS) instead of one new J-2X engine, and 3 man-rated ablative nozzle RS-68 main engines instead of 2 new regeneratively cooled nozzle RS-68 main engines. The Jupiter 120 Crew LV in the revised DIRECT 2.0 proposal specifies the use of 2 existing man-rated ablative nozzle RS-68 main engines instead of 2 new regeneratively-cooled nozzle RS-68 main engines.
Proponents of the DIRECT 2.0 proposal argue that the additional performance capacity of the Jupiter 120 Crew LV proposal over the Ares I Crew LV provides sufficient performance margin to substantially increase crew safety through more robust safety systems, including several tons of protective armor between the Orion spacecraft and the fuel and engines of the core stage. Proponents also argue that the use of existing, flight-proven systems derived from the Space Shuttle and Delta IV EELV in DIRECT 2.0 is inherently much safer than the untested new components that would need to be developed for either Ares I or the original DIRECT proposal.
DIRECT 2.0 was further expanded in September 2007 with a 130 page study, covering 9 months of refinement into the concept, at the AIAA "Space 2007" Conference in Long Beach, CA. in which the launch vehicles were presented as a single part of a much wider reaching architecture enabling the US to maintain the ISS, progress on to the moon with larger missions than Ares I and Ares V can perform, and presented the wide range of options available to evolve the program using DIRECT launchers to achieve the goals of the Mars program which will follow eventually. The paper also considered many other options which are enabled by DIRECT, such as Lagrangian point staging architecture options and mission architectures for visiting Near-Earth object destinations.
[edit] References
[edit] External links
- DIRECT Launcher proposal website
- v2.0.1 Updated PDF Baseline Proposal
- AIAA Space 2007 Conference presentation in High Res or Low Res
- TheSpaceReview.com commentary on ESAS including DIRECT
- TheSpaceReview.com article about DIRECT
- DIRECT v1.0 discussion on NASASpaceFlight.com (now locked at 131 pages)
- DIRECT v2.0 discussion on NASASpaceFlight.com (now locked at 250 pages)
- DIRECT v2.0 Thread 2 discussion on NASASpaceFlight.com (current discussion ongoing)
- TeamVision page about DIRECT
- Q&A: ESAS Lead - Dr Doug Stanley (On DIRECT)
- TheSpaceShow.com interview about DIRECT, 07/01/2007 issue
- TheSpaceShow.com interview about DIRECT, 02/17/2008 issue and related presentation in PDF
