In Part 1, we looked at the pieces strewn about our living room floor. In Part 2, we examined the Goals and Destinations in Chapter 3.0. And in Part 3, the three current Human Space Flight programs were reviewed (International Space Station, the Space Shuttle and the Constellation Program).
Chapter 5.0 Launch to Low-Earth Orbit and Beyond
In this section, The Augustine Commission examines launch vehicles. We begin with the opening statement, with which we agree:
Launch to low-Earth orbit is the most energy-intensive and dynamic step in human space exploration. No other single propulsive maneuver, including descent to and ascent from the surfaces of the Moon or Mars, demands higher thrust or more energy or has the high aerodynamic pressure forces than a launch from Earth. Launch is a critical area for spaceflight, and two of the five key questions that guide the future plans for U.S. human spaceflight focus on launch to low-Earth orbit: the delivery of heavy masses to low-Earth orbit and beyond; and the delivery of crew to low-Earth orbit.
5.1 Evaluation methodologies for Launch Vehicles
The Commission used “cost, performance and schedule parameters, as well as safety, operability, maturity, human rating, workforce implications, development of commercial space, the consequences to national security space, and the impact on exploration and science missions”. They note that some of these are quantitative and some are qualitative measures. Evaluations of the claim for each launcher was made and adjusted, and the uncertainty was assessed. Historical bounds were employed where appropriate. Some 70 lower-level metrics were used to construct 13 top level metrics.
5.2 Heavy Lift to Low-Earth Orbit and Beyond
The Commission began by reiterating the Constellation plan to loft about 600 metric tons (mt) per year to low Earth orbit (LEO). By comparison, NASA launched 250 mt per year during Apollo and the International Space Station (ISS) has a mass of about 350 mt.
Figure 5.2-1 listed the five candidates and their lift to LEO (see Launch Vehicles for visuals) and Figure 5.2.1-1 gave Trans Lunar Injection (TLI) with no refueling and with in-space refueling:
|Launch Vehicle||LEO||TLI no refueling||TLI in-space refueling|
|EELV Super Heavy||75 mt||26 mt||55 mt|
|Directly Shuttle Derived||100-110 mt||35 mt||75 mt|
|Ares V Lite||140 mt||55 mt||120 mt|
|Ares V||160 mt||63 mt||130 mt|
|Ares V plus Ares I||185 mt||71 mt||150 mt|
Notice that the Commission has brought the potential of in-space refueling front and center, either as propellant transfer from one spacecraft to another (as in a dual launch Ares V Lite or Jupiter 246), or from a true propellant depot, which would be supplied by commercial contract. However, “the Committee found both of these concepts feasible with current technology, but in need of significant further engineering development and in-space demonstration before they could be included in a baseline design”. Thus, the initial set of evaluations would need to examine the mass that an Earth Departure Stage (EDS) could push through TLI without refueling.
A detailed study of launch reliability of multi-launch missions commissioned by the Committee concluded that at most three critical launches be used. Reasonable chances for success required 90+ days of on-orbit life for an EDS or propellant depots.
Subsequent to Shuttle retirement, the need for NASA to launch 400 to 600 mt to LEO each year would consume much if not all of the existing and planned excess EELV capacity. Further, it would be expensive.
Finally, the Commission notes that heavy lift vehicles “would allow large scientific observatories to be launched, potentially enabling them to have optics larger than the current five-meter fairing sizes will allow. More capable deep-space science missions could be mounted, allowing faster or more extensive exploration of the outer solar system”.
All the foregoing was seen as justification for the development of Heavy Lift vehicles. The Commission then reviewed the choices in the chart above.
Ares V: This is the most capable of the proposed rockets. Together with the Ares I, it can launch 185 mt to LEO, 71 mt through TLI and land 14 tons of cargo only on the lunar surface, or 2 mt of cargo plus crew. Ares V requires expansion of the External Tank (ET) to 10 meters, the development of new 5.5 segment solid rocket motors (SRM), development of a regenerative version of the RS-68 engine and the development of the J2-X second stage engine (modified from the Saturn J2 engine).
Ares V Lite: Ares V Lite is a derivative of the Ares V, but with an LEO payload of 140 mt. This rocket would require the completion of the 5 segment SRM under development for Ares I. The remaining new Ares V components would still require development. For lunar missions, the Ares V Lite would be human-rated and used in the “dual mode”. In single launch it can place 14 mt of cargo on the lunar surface, and with a larger Lander than Ares V, it can land 5 mt of cargo plus crew.
SDLV Side-Mount: The side-mount and the in-line SDLV both use the existing Space Shuttle ET, the 4 segment SRM and the Space Shuttle Main Engines (SSME). The side-mount replaces the Shuttle with a cargo pod. The Committee combined the side-mount with the in-line variants for purposes of evaluation. They did note, however, that “the side-mount variant is considered an inherently less safe arrangement if crew are to be carried, and is more limited in its growth potential”.
SDLV In-Line The in-line variants are represented by the Jupiter family of rockets, as proposed by the Direct team. The Committee assumed that three Jupiter 241 vehicles would be used for a lunar mission, and that 5 mt of cargo could be landed with crew. No figure was given for a cargo only dual-launch mission, but the report states that more than 20 mt of cargo can be landed by a single Jupiter 241 using in-space refueling. Now, the three launch scenario is peculiar. Perhaps the Commission was trying to replicate the LEO loft mass of a dual Ares V Lite mission (2 x 140 mt). However, that much fuel, lander and crew far exceeds the Constellation Program (CxP) requirements. Furthermore, Ross Tierney, from Direct, has stated that “the right 2-launch Jupiter architecture is actually capable of landing 19mT of useful payload mass on the lunar surface every crew mission…Given that the Ascent Module only consists of about 6.4mT of that, this architecture is actually capable of landing almost the same 14.5mT* cargo modules as CxP are currently planning to land using cargo-only missions”. So we are left with unanswered questions concerning the assumptions and evaluations made by the Commission, not only about SDLV, but the Ares mission architectures.
EELV Super Heavy The Extended Expendable Launch Vehicle (EELV) is represented by the Atlas 5 Phase 2 Heavy, which consists of the core rocket plus two boosters of the same basic design along with an upgraded common upper stage (to be used by both Atlas and Delta). The common upper stage would use four RL-10 rocket engines, which have a long history of successful flights aboard Titan, Delta and Atlas among others. This configuration is capable of lofting a maximum of 75 mt to LEO. A dual launch configuration with in-space refueling is capable of conducting Flexible Path missions.
Summary of Findings
- Heavy Lift capability is beneficial to human exploration as well as national security and the scientific community.
- In-Space refueling represents a significant benefit to space transportation systems beyond low Earth orbit. It requires development and would not be on the critical path. A prudent approach is to develop Heavy Lift capable of early missions and phase in in-space refueling when it becomes available.
- A new emphasis of sustainable operations is needed. “NASA’s design culture emphasizes maximizing performance at minimum development cost, repeatedly resulting in high operational and lifecycle costs. A shift in NASA design culture toward design for minimum discounted life-cycle cost, accompanied by robustness and adequate margins, will allow NASA programs to be more sustainable”.
- In-Space Propulsion for missions beyond LEO that last for weeks or months require stages using efficient engines with high-reliability restart capabilities.
The Lunar Surface Capabilities of the various systems are compared in the following table:
|Launch Vehicle||LEO||Cargo Only||Cargo and Crew|
|EELV Super Heavy||75 mt||NA mt||NA mt|
|Directly Shuttle Derived||100-110 mt||14 mt*||5 mt*|
|Ares V Lite||140 mt||14 mt||5 mt|
|Ares V plus Ares I||185 mt||14 mt||2 mt|
5.3 Crew Launch to Low-Earth Orbit
Crew safety is an overriding issue in human space flight. The safe delivery of crew to LEO and their return is critical. This is the fourth key question (see Part 1) that the Committee examined. The assumed that Orion would be the crew vehicle, and that the launch vehicle would either be government provided and operated, or a commercial service.
Ares I was selected in 2005 as part of the ESAS study, and was expected to be operational in 2012. The Constellation program now projects initial operational capability (IOC) in 2015, and the Committee thinks this will slip further. Both budgetary and design problems have been encountered.
International Transportation was deemed acceptable by the Committee. However, sustained U. S. leadership in space requires domestic crew launch capability.
A human rated EELV was considered by the Commission. An independent study found that the launch of Orion on the Delta IV Heavy was technically feasible, but the long term development and carrying costs offset any savings versus Ares I.
Commercial Transport of crew to LEO is a hot topic. The Committee asked “can a simple capsule with a launch escape system, operating on a high-reliability liquid booster, be made safer than the Shuttle, and comparably as safe as Ares I plus Orion”? A number of factors were considered:
- A strong role for NASA oversight of the development would be required.
- The cost to NASA of underwriting design, development, test, and evaluation (DDT&E).
- The potential non-NASA uses of LEO crew transport
The Committee made several estimates of total costs, and arrived at a preliminary estimate of $5 Billion dollars. Assuming a “less-constrained” NASA budget, a commercial LEO crew transport service could be available by 2016.
Finally, the Committee assessed the risks to the human space flight program associated with commercial crew transport. Such development could distract from the near-term goal of developing commercial cargo capability. The commercial community might fail to deliver a crew transportation system. The fall-back position for NASA would be human rating the Heavy Lift Vehicle. The Committee assumes that the first stage of the HLV will be developed as quickly as possible. We leave the implications of this statement as an exercise for the reader.
5.4 Additional Issues in Launcher Selection
Launch Vehicle Performance and Costing The factors in this section include:
- Evaluation of the claimed cost, schedule and performance of the various launch vehicles.
- The advantage of shifting to commercial purchase of space transportation systems.
- The loss of the workforce and expertise built up within NASA from shifting to commercial sources.
- The health and viability of the solid rocket motor industry from all-liquid fuel launch vehicles.
Launcher Reliability The Committee reviewed the historical reliability of the Shuttle, Saturn, Titan, Delta and Atlas programs. Launchers derived from existing systems have shown greater reliability in early stages of development than newly developed systems.