User:Fotoguzzi/DIRECT faq

DIRECT FAQ
 What is DIRECT?

A: DIRECT is an architecture of launch vehicles, spacecraft and mission plans which describes how missions to the Moon, Near Earth Objects, Mars and even beyond may be accomplished. It is broadly comparable to NASA's Constellation Program (CxP).

Q: What is Jupiter?

A: Jupiter is a family of heavy lift launch vehicles used by DIRECT, and based around a single Core stage which maximizes heritage from the Space Shuttle and its infrastructure.

Although DIRECT assigns some medium-lift tasks to EELV's, Jupiter mostly fills the roles of Ares I & Ares V in CxP.

Q: What do all the letters and numbers mean (J-130, J-246, etc)?

A: J stands for Jupiter, the Direct heavy launch vehicle.

The first digit is the number of stages on the rocket. The Jupiter can be flown as either a one or two stage launch vehicle.

The second digit is the number of engines on the first stage. For Direct 3.0 these are all SSME’s- the same engine that is on the Space Shuttle.

The third digit is the number of engines on the second stage. For single stage rockets, this is zero. For Direct 3.0, there are a number of different possible engines that could be used to power the second stage.

All versions of Jupiter also have Solid Rocket Boosters, like the Shuttle.

Q: What are the various configurations of Jupiter?

DIRECT Phase 1 builds the J-130. It consists of a single stage, the Core, based closely on Shuttle's External Tank & 3 SSME's. With a pair of SRB's, it can fly 65-75mT of Orion (crew) and/or cargo to various Low Earth Orbits, including the Space Station. This is much more than any vehicle currently flying, including the Shuttle.

DIRECT Phase 2 then adds a fourth engine to that Core, and an Upper Stage. This can lift 100mT or more to orbit. Two such vehicles can fly NASA's planned Lunar missions, but with greater safety and with performance to spare.

Q: What are the options for the Upper Stage?

Jupiter's Upper Stage (JUS) is an enlarged version of an existing design. NASA could choose to power it with any of the following engines, based on their detailed requirements:-

Six RL-10b's, making J-246 - the recommended option. This engine has both a superb flight history and high performance. It only requires safety enhancements for crewed flights, which is likely to happen for the Lunar mission anyway.

Six or seven RL-10a's, making J-246 or J-247. Another variant of the ubiquitous RL-10, as above. Unfortunately, both these engine options have workable "J-246" variants.

A single J-2X, making J-241. This is NASA's engine choice for its Ares I & Ares V Upper Stages, but much development work is still outstanding and exact performance is in doubt.

Four RL-60's, makes J-244. More powerful version of the RL-10. Development currently on hold, and least ready of all the engine options, but has perhaps the most long-term potential.

Q: What is J-24x?

Most of the discussions about two-stage Jupiter are equally applicable whatever Upper Stage engine is used. The "x" denotes this, i.e. is shorthand for "J-241 or J-244 or J-246 or J-247".

Q: What is J-1x0?

As above, but encompasses both J-130 and its two-engine sibling J-120.

J-120 can lift about twice the payload of an EELV to LEO, but doesn't have the safety margins for crewed flights. It's most likely to be used for deep-space probes and low mass, but bulky items.

Q: What about the H at the end?

A: The H at the end stands for heavy. The Ares rockets currently being designed by NASA require larger solid rocket boosters than what the space shuttle currently uses. Direct does not require these heavier 5 segment boosters, but data summary sheets have been prepared to show that it can utilize them. For most configurations, they improve the payload to low earth orbit by about 10-15 metric tonnes, and the payload through TLI by over 12 metric tonnes.

Q: Why are there so many different technical data summaries?

A: The Jupiter rocket is a versatile design, which is meant to be flown with one or two stages, with or without a crew.

In addition, it is still in the planning stage, so we have summarized the performance of a number of different possible configurations. The vast majority of these will never be flown, but the data for all of them is necessary to determine which is the best one to use.

If that isn’t confusing enough, all rockets have different performance based on what function they need to perform and what orbit they need to reach. Several rockets have multiple data summaries for different orbits, as the starting orbit used to leave for the moon is different to the International Space Station’s orbit.

Q: What is the CLV?

A: Crew Launch Vehicle - any vehicle carrying Orion and crew. This may be J-130 or J-24x, and may be bound for LEO/ISS or the Moon/further afield.

Crew Launch Vehicle always flies with a Launch Abort System, which should carry Orion and the crew clear if the Jupiter explodes, as happened to Space Shuttle Challenger.

If bound for ISS, the CLV is likely to also carry cargo.

If bound for an exploration mission (Moon, etc), the CLV will also include the Altair Lunar Lander.

Q: What is the CaLV?

A: Cargo Launch Vehicle - any vehicle carrying cargo and not carrying crew. Again, this may be J-1x0 or J-24x, and may be bound for LEO/ISS or the Moon/further afield.

If bound for an exploration mission (Moon, etc), the CaLV's payload will be the Altair Lunar Lander, and possibly some EDS fuel.

Q: What is an EDS?

A: Earth Departure Stage. Sending spacecraft such as Orion & Altair from LEO towards the moon requires lots of fuel - more mass of fuel than the mass of the spacecraft, in fact.

J-24x is able to carry a payload into LEO which is purely fuel. It can do this because the Upper Stage tanks are 2-3x larger than required just for the vehicle to reach orbit. This is a very efficient way to lift the maximum possible fuel into orbit.

The Upper Stage then docks with Altair & Orion and burns that fuel payload to perform Trans-Lunar Injection (TLI) - the escape from Earth's gravity and towards the Moon.

See the "TLI Payload Performance" figure on the EDS baseball cards for how much mass can be pushed towards the Moon, and that's almost all Orion & Altair. For comparison, NASA's current TLI requirement is 71.something mT.

Q: How does DIRECT's crewed Lunar mission work?

A: About five days before TLI, a J-24x EDS flight launches to a height of about 130 Nautical Miles (nmi). It then "loiters" in orbit.

Within the next four days, a second J-24x CLV (Altair + Orion + crew) launches to the same orbit and rendezvous’.

EDS docks underneath the Altair and Orion docks on top of the Altair (this may actually happen before the EDS docking).

The EDS / Altair / Orion stack then waits for the appropriate moment before EDS performs its TLI burn. Once the burn is complete, EDS detaches and is discarded.

Q: How does this compare to NASA's current plans for their crewed lunar mission?

A: About five days before TLI, an Ares I launches Orion + crew to a height of about 130 Nautical Miles (nmi). It then "loiters" in orbit.

Within the next four days, Ares V launches both an Altair and EDS to the same orbit.

EDS is already docked underneath the Altair, so no docking is required for this.

From this point on, DIRECT's mission is identical to NASA's.

Orion docks on top of the Altair, EDS / Altair / Orion stack performs its TLI burn at the appropriate moment, and EDS is discarded after TLI.

Q: How does DIRECT's cargo Lunar mission work?

A: Very similar to the crewed mission.

J-24x EDS launch is identical.

Altair launch is similar to the crewed mission, except only requires a cheaper / simpler J-130 instead of J-24x.

As with crew, Altair docks on top of the EDS, the EDS / Altair stack performs its TLI burn at the appropriate moment, and EDS is discarded after TLI.

There is also an option to launch a single J-24x with a partial fuel load and a lightly-loaded Altair. Whilst this can land some payload on the moon, two-launch cargo lands much more, and only requires one very expensive Altair lander, so is cheaper per Kg.

Q: How does this compare to NASA's current plans for their cargo Lunar mission?

A: DIRECT's single-launch cargo mission is identical to NASA's cargo mission.

Because of the launch capacity of Ares V, it can land more payload than DIRECT's single-launch mission, but not as much (or as cheaply) as DIRECT's dual-launch.

Q: Is Direct safe?

A: All spaceflight is dangerous. Enormous amounts of energy must be released in a fairly short period of time to put people into orbit. Although this is inherently risky, the majority of the risk to the crew is actually after leaving Earth orbit, when abort back to Earth is much more difficult.

That being said, Direct is less dangerous than many alternatives. The Jupiter rocket uses existing engines, which are known to be reliable. In some cases, it is able to reach a safe orbit in the event of a liquid engine failure and complete TLI in the event of a second failure. It relies on relatively little new unproven technology, minimizing the risk of nasty surprises that have increased the cost and schedule of the Ares rocket.

Because the crew is mounted on the top of the launch vehicle, a Launch Abort System can eject the capsule from the rocket in the case of a catastrophic failure. The flight profile of Jupiter is less aggressive (lower max. acceleration and dynamic pressure) than that of other launch systems, making it easier for the LAS to do its job.

There are more subtle benefits as well. The Direct program intends to merge space shuttle operations into Direct test flights and Direct operations continuously. And much of the Direct hardware is similar to that of the Shuttle. The contribution of human error to risk cannot be understated. By keeping the current operations team running, loss of institutional knowledge and the risk of learning new systems is minimized, and the ‘learning curve’ for the new rocket is flattened.

Crew risks are actually much higher after the crew have left Earth orbit, whilst abort back to Earth is much more difficult.

DIRECT has the performance to carry much heavier spacecraft, which should avoid the need for the designers to choose between weight savings and safety features.

Q: Is Direct affordable?

A: Direct minimizes expensive new development programs by reusing existing engines and using variations of one rocket for all missions. In addition, it can be built in existing manufacturing facilities, assembled in the existing VAB, and transported using existing crawlers and barges. Because fixed costs and development costs are a large proportion of a total program budget, minimizing these is more effective than minimizing the actual manufacturing costs of each individual launch vehicle. Economies of scale are important, and Direct finds these by using one rocket for a variety of tasks.

Q: is Direct sustainable?

A: The versatility of Direct allows it to be used for a wide variety of tasks, from science to space stations, to lunar, asteroid, and even Mars destinations. As long as NASA and its international partners are embarking in missions more ambitious than the Gemini program of the 1960’s, Direct will be adaptable and appropriate to the task.

'''Q: You call your project Direct 3.0. Was there a Direct 1.0 and 2.0? What happened to them?'''

A: The progression from Direct 1.0 to Direct 2.0 took place in late 2006/early 2007 as a result of NASA being unhappy with some features. The details of this change are available in the Direct 2.0 FAQ.

In early 2009, it became evident that the "ablative" RS-68 engines designed to power the core stage of both Ares V and Direct 2.0 were not suitable. The RS-68 powers the unmanned Delta IV system. It is perfectly safe on that vehicle, but studies suggested that it would not be able to survive the thermal environment associated with the large solid rocket motors and it required a costly & lengthy development program. To circumvent these problems, the design team chose to switch to the SSME which powers the space shuttle.

Because the SSME is more efficient than the RS-68, the first stage has better performance, and a smaller upper stage is required. This has advantages for the payload which can be pushed through TLI, and allowed the use of smaller, existing upper stage engines like the RL-10. As a result, the development of the J2-X is no longer necessary to build the upper stage. That is Direct 3.0

Q: What is the SSME?

The SSME is the Space Shuttle Main Engine. This engine has been flying for thirty years. The engine is ready for test flights of the Jupiter right now. The SSME enables the Jupiter to use the RL-10 engine for the upper stage. That means that we have the potential to go all the way to the moon with 'NO' new engine development.

Since the Ares program was started in 2005, the Ares V has switched engines several times (RS68 is the ablative engine and RS68r is the regenerative engine, where LH2 circulates through the skirt before being burned, just as the SSME does):

Timeframe             Ares         Jupiter Post ESAS             SSME       SSME Direct 1.0            RS68        RS68r Direct 2.0            RS68        RS68 Direct 3.0            RS68r       SSME

The Direct team has adjusted its choice as data has become available.

Recently, base heating analyses showed that the RS68 ablative options were not viable for Ares V and, and at this point DIRECT returned to SSME. See additional information in the Base Heating Problem question.

With regard to cost, if you put the SSME into "mass production", say at least 12 per year, you can get that per-unit price down. The cost for totally standard SSME Block-IIA units, as flown on Shuttle, could drop to more like $40m per unit in the production numbers we need for the early Jupiter program (averaging 16/yr thru ~2017).

By the time the Jupiter Program ramps up (we're aiming to fly twelve Jupiter 24x's per year = 48 SSME's per year), we would like to get a cheaper, expendable variant developed to drop that cost to more like $30m per unit by 2020.

Ares-V now has to use a Regeneratively Cooled Nozzle to survive the Base Heating Environment. That limits the choices to either go to SSME like Direct 3.0 has, or to choose to re-develop the RS-68 into a Regen system. The version they would need would be the RS-68 Regen (Human Rated, 108% Thrust, Regen Nozzle) and it is expected to cost around $25m each.

At this level, the cost differences per engine are negligible compared to verall costs per launch.

Q: What is the Base Heating Problem?

Base Heating is heating of components at the base of a rocket due to engine exhaust. Also, some engines use gas generation to power the turbopumps, which burn gaseous fuel and oxidizer, and the exhaust is also dumped into the base area. If the heat becomes too great, components can fail.

On the Delta IV (DIV), which uses the RS68, you get airflow around each Core -- even between the Cores on the Heavy. And the engine nozzles are never more than about 3ft away from the airflow, so the that doesn't allow much space for heat to build-up in a low-pressure area below the stage.

The 8.4m diameter of the Jupiter (or 11m in the case of the new Ares-V) punches a much bigger hole through the air. This causes two problems. First it creates an area of very low pressure all around the engines and the recirculating gasses caused by Plume induced Flow Separation (PIFS) are "attracted" into that area because of that. Second, the larger diameter means that less air flows down around the engines to 'push' the collecting hot gasses away from that area, so the heat simply builds and builds in that region.

The Base Heating problem was the reason Ares V moved to the RS68 regen in 2009. Since Ares V abandoned the RS68 due to Base Heating problems, the Direct Team followed suit, returning to the SSME, which was the original choice made by ESAS.

A Regen RS-68 cannot be made operational before 2016 at the very earliest. That would then determine the earliest possible IOC date if you go down the RS-68 path. But SSME is ready to start test flights right now. From a schedule perspective, there has been no question for Direct 3.0 about using the SSME.