The Shuttle-Derived Heavy Lift Launch Vehicle, also known as the High Confidence Heavy Lift Launch Vehicle (or even variations of the "Side Mount Launch Vehicle" or "HLV" or "Not-Shuttle C") is an alternate launch vehicle proposal for the NASA Constellation program. It was first presented on June 17, 2009 by John Shannon, NASA's Shuttle Program manager, to the Augustine Commission which is tasked to review NASA's human spaceflight program.
It is based on the Shuttle-C concept which has been the subject of various studies since the 1980s. Derived from the currently used Space Shuttle hardware, it is proposed to replace the winged Orbiter from the Space Shuttle stack with a simple not-winged side-mounted payload carrier. The designs of the STS' External Tank (ET) and the 4-segment Shuttle Solid Rocket Boosters (SRBs) shall be reused.
According to NASA's John Shannon the HLV can be developed within 4 1/2 years until the first manned flight occurs. The development program should cost about USD 6.6 billion, which is only about 20% of the costs currently estimated for the Ares I and Ares V vehicle development.
An unmanned side-mounted concept of the Space Shuttle named Shuttle-C was the subject of various concepts that were investigated between 1984 and 1995. After the Space Shuttle Columbia accident a two-year industry study was prepared in 2004 and 2005 to further investigate the concept in order to replace the Space Shuttle. The Exploration Systems Architecture Study (ESAS) in 2005 also investigated a Shuttle-C option for Project Constellation, however again only in an unmanned version. All these concepts included the side-mounted carrier to be an autonomous spacecraft which would detach from the External Tank after main engine cut-off similarly to the Space Shuttle. Some of the studies included the reuseability of the Space Shuttle Main Engines on this side-mounted carrier. None of the concepts involved in ascent fairing separation.
The Shuttle-C concept as a cargo only option was not funded in the 1980s and 1990s due to NASA's budgetary constraints. The 2004-2005 industry study provided an updated proposal, which was looked at by ESAS but was ultimately deemed inferior to the Ares I and Ares V option. Crewed side-mounted Shuttle-C concepts were not looked at at all in ESAS.
The HLV proposal presented by John Shannon on June 17, 2009 is partly based on the original Shuttle-C proposal but differs considerably from it, mainly due to not using the side-mounted carrier as a separate spacecraft which detaches from the ET and due to proposing to also carry crews on the HLV, not just cargo. The team involved in analysing and designing the HLV design at NASA include about 60 NASA engineers headed by Rick Manella.
The HLV is proposed to be a 4,600,000 lb vehicle at liftoff with two 4-segment Space Shuttle Solid Rocket Boosters weighing about 2,600,000 lb providing a total thrust of 5.9 Mlbf at sea level, with the currently used Space Shuttle External Tank weighing about 1,660,000 lb in a fueled stage and a propulsion and payload carrier side-mounted to the vehicle.
This side-mounted carrier includes a boattail carrying the propulsion elements which include 3 Space Shuttle Main Engines weighing about 57,000 lb in total and the 7.5m diameter payload carrier with a separable fairing weighing 51,000 lb. The basic vehicle does not require an upper stage. Orbit circularization for missions to lower Earth orbit or trans-lunar injection burns for missions to the Moon or other destinations outside of Earth orbit are provided by the payload which detaches from the HLV after the main ET fuel is depleted.
The only completely new hardware development required for the HLV is the side-mounted carrier. All other components used on the HLV are currently in use with the Space Shuttle. According to John Shannon's proposal the first several flights (up to 6 flights) of the vehicle will reuse spare parts of the current Space Shuttle fleet and salvage functioning hardware from the orbiters, including existing Avionics modules, the Flight Software and the Space Shuttle Main Engines (SSMEs) (Block I flights). Virtually no change to the current Space Shuttle infrastructure, from the Vehicle Assembly Building to the External Tank barge to the launch pads is required.
Although technically not part of the HLV, the proposal envisions that the upper stage which is attached to the payload and rests in the payload fairing for launch shall be a J2-x engine currently being developed for the Ares I launch vehicle. It provides nearly 300,000 lbf (vacuum) and has a specific impulse (isp) of 448 sec. Alternatively The United Launch Alliance has proposed that their The Dual Thrust Axis (Lunar) Lander (DTAL) could fit in a side mount payload shroud .The United Launch Alliance proposed ACE 41 and ACE 71 upper stage/fuel depot could also fit inside a side mount payload shroud and the ACE 71 at 75 metric tons is well within the side mount shuttle derived vehicles payload capacity .This could eliminate the need for evolving the directly shuttle derived vehicle when combined with a fuel depots architecture.
The HLV's 4-segment SRBs deliver a specific impulse (isp) of 267 sec and a thrust of 5.9Mlbf and burn for about 155 seconds. The SSMEs shall be flown at 104.5% and deliver a specific impulse (isp) of 452 sec and 1.5 Mlbf (vacuum) and burn for about 500 seconds (depending on the mission profile). The payload mass for different missions are as follows:
In contrast to prior proposals of Shuttle-C, except for the 4-segment SRBs no part of the vehicle is recoverable and reusable. The HLV uses a different flight profile than the Space Shuttle because no loads on wings have to be considered. The payload fairing (23,000 lb) is jettisoned after 185 seconds into the flight at about 57 nautical miles altitude (above 100 km altitude) in order to improve payload mass of the vehicle. The used SSMEs are not reused and thus can be simplified, but will have to be produced for each vehicle (unlike the Shuttle). For lunar missions, the HLV proposal envisions suborbital staging at 30 nm x 120 nm of the vehicle to increase mass through TLI (trans-lunar injection) with two burns of the upper stage (a suborbital burn and an additional TLI burn).
While the HLV is designed to provide crew and cargo missions to the ISS, its primary aim is to replace the Ares I – Ares V lunar architecture. The rudimentary mission architecture presented by John Shannon uses a pure Lunar Orbit Rendezvous profile. Two HLVs are launched for the completion of one mission. The first HLV is launched with the lunar lander and immediately places the lunar lander on a trans-lunar injection path. The lunar lander can have a net mass of 35 metric tons after TLI and by itself inserts into a low lunar orbit (LLO). According to John Shannon's presentation in LLO the lunar lander will weigh about 28 metric tons (after burning fuel to get there).
In a second launch, the crew on the Orion spacecraft is launched on a HLV and also immediately propelled to trans-lunar injection. The 20 metric ton Orion spacecraft will however remain attached to the upper stage which inserts the Orion spacecraft into low lunar orbit where it docks with the lunar lander.
The NASA presentation shows that the HLV has limited growth options to take more payloads into space. While 5-segment SRBs can be used on the vehicle, they will require significant re-engineering of the vehicle and will only yield 7 metric tons more to lower Earth orbit. Other growth options include an upgrade of the SSME to 106% or 109% thrust level and a switch from the J2-x upper engine to an airstartable SSME.
NASA's presentation mentioned the following benefits and disadvantages of the HLV proposal: