DIRECT
From Wikipedia, the free encyclopedia
- For other uses, see Direct.
| Fact sheet | ||
|---|---|---|
| Function | Manned and unmanned partially re-usable launch vehicle | |
| Manufacturer | NASA Alliant Techsystems Boeing Integrated Defense Systems Lockheed Martin Pratt & Whitney, Rocketdyne United Space Alliance |
|
| Country of origin | USA | |
| Size | ||
| Height | 85 to 90m | |
| Diameter | 8.41 m (identical to Shuttle External Tank) (27ft 7in) | |
| Mass | 2,125,975kg (4,686,973lb) [Lunar Crew LV GLOW] | |
| Stages | 2 or 3 | |
| Capacity | ||
| Payload to LEO | 62,500 to 137,500 kg (137,500 to 302,500 lb) | |
| Payload to Trans-Lunar Injection |
approx 38,000 kg (more with growth options) | |
| Launch History | ||
| Status | Proposal | |
| Launch Sites | LC-39, Kennedy Space Center | |
| Notable payloads | Orion EDS LSAM |
|
| Boosters (Stage 0) - Solid Rocket Boosters | ||
| 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 - Core stage, based on Shuttle External Tank | ||
| Engines | (2 RS-68 "Regen") | |
| Thrust | 7,324 kN (1,646,400 lbf) | |
| Specific Impulse | 435.5 sec | |
| Burn time | 521 sec | |
| Fuel | LOX/LH2 | |
| Second Stage (Heavy Variant) - EDS | ||
| Engines | 1 J-2X | |
| Thrust | 1,217 kN (273,500 lbf) | |
| Specific Impulse | 450.0 sec | |
| Burn time | 260 sec | |
| Fuel | LOX/LH2 | |
DIRECT, named to emphasise its direct heritage to the existing Space Shuttle design, is a proposal to NASA for an alternative Shuttle Derived Launch Vehicle to the currently planned launch vehicles being designed currently for the new Vision for Space Exploration missions heading to the Moon, Mars and beyond.
The proposal is fundamentally to replace the two Ares launch vehicles, with one single launch vehicle capable of performing both missions, thereby cutting costs and reducing schedules.
It is 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. 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.
Contents |
[edit] Design
The DIRECT launch vehicle concept consists of a core stage, based on many existing elements of the current External Tank with a pair of 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. Initial performance to Low Earth Orbit (LEO) [specifically to 60x160nm, 28.5degree inclination initial orbit] for this initial variant of the DIRECT Crew LV is conservatively expected to be at least 62,500kg (138,000lb), which is 323% of Ares I's 19,300kg (42,500lb) maximum performance.
To speed development, the RS-68 engines would initially be man-rated versions of those used successfully on the current Delta 4 program. DIRECT plans to perform a relatively routine upgrade to these engines by replacing the existing ablative nozzle with a Regenerative Cooling Nozzle, which will allow the engine performance and efficiency to both be increased by approximately 5%. With this upgrade, Crew LV payload performance to LEO increases to 70,900kg (156,000lb) - 367% of Ares I's performance. This means that an Orion spacecraft could be launched on top of the vehicle, along with 48,900kg (108,000lb) 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 the already-planned Pratt & Whitney/Rocketdyne J-2X engine would be used to increase payload capacity for certain missions. Payload performance to LEO increases to at least 98,200kg (216,000lb).
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, one DIRECT Crew and one DIRECT Cargo flight together, are capable of launching 169,100kg (373,000lb) which equates to a 12% increase in overall Lunar mission performance.
[edit] Design History
The basic concept is not new. It 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 brough 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.
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.
This resulted in the basic design of the DIRECT launch vehicle. But this is not the complete story.
[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.
