Few days ago I asked former NASA astronaut Bruce McCandless II to share his ideas about last shuttle mission with the Jam-eJam online Science. He wrote the following review for me and I published its Persian translation at Jam-e-Jam online.
You can find his original English version here:
Bruce McCandless was travelled into space 2 times with Space shuttles Challenger and Discovery. In STS-41 B, he marked the first Manned Maneuvering Unit (MMU) and during his 2nd flight in STS-31 he was member of crew of Discover who delivered Hubble Space Telescope into the Orbit. Here is his review for Jam-e-Jam.
Space Shuttle Overview
by Bruce McCandless II
4 July 2011
Any “Space Shuttle retrospective” must start by recalling that the program was originally The National Space Transportation System. Here the word “the” in reality meant “the one and only” and “national” expanded its scope to include all U. S. launch customers. Consequently, the NSTS (as it was called) was to have been the only way into space for U.S. customers (NASA, military, NOAA, commercial, scientific – everybody), and also sought to capture as much of the international market as possible. It was on this basis that initial projections showed 500 launches in the first ten years of operations – roughly one per week! This author is skeptical that the 50/year rate could have been achieved, but believes that, perhaps, 25/year would have been realistic. These high flight rates were necessary to justify the claimed reduction in cost per pound (or kilogram) launched by a factor of ten. The big divisor was needed to reduce the fixed costs (aka the “standing army”) to an acceptable cost per launch.
The CHALLENGER Accident (STS 51-L) changed all that in two ways. First, the investigating commission, led by former Secretary of State William P. Rogers, recommended that NASA not risk human lives (the crew) by carrying payloads that could be carried on unmanned rockets or by carrying non-essential “space flight participants,” such as a teacher, journalist, or government official. Second, the 2½ year-long hiatus in Shuttle operations associated with the post-accident engineering improvements required the introduction and use of alternative launch systems, such as the Titan-34D “Contingency Launch System” to fill the gap. From that point in time onwards there was never the prospect of enough demand to make the Shuttle financially viable.
That said, the Space Shuttle has been a truly remarkable technological achievement:
1) It was (and is) the world’s first mostly reusable launch system, undertaking a total of 135 missions.
2) It provided a major “cargo return from orbit” capability not approached by any other system, and landed on a runway!
3) It featured the highest performance, reusable, throttlable, liquid hydrogen / liquid oxygen rocket engines.
4) As the first large, totally digital, “fly-by-wire” aircraft, it pioneered the technology of redundant, “real time” computer control easing the acceptance of current aircraft such as the Boeing 777, Airbus A320, and later models.
5) Its ability to carry a large crew (up to 8 persons) with consumables and privacy facilities accommodated both mixed-gender crews and up to five EVA’s (“spacewalks”) on missions such as those servicing the Hubble Space Telescope.
6) It pioneered a new heat protection system in which the TPS (Thermal Protection System) tiles radiated heat back out through the boundary layer, instead of “sluffing off” (ablating) material to carry away heat.
7) It demonstrated the capability to retrieve small satellites from LEO (e.g., WESTAR 6 and PALAPA B-2) and to repair / refurbish assorted satellites (e.g., Solar Maximum Observatory, SYNCOM IV-3, INTELSAT VI-F3).
On the negative side of the ledger, the Space Shuttle lacked an effective escape system. After the first four test flights, which had ejection seats for their two-man crews, NASA relied on the assertion that it was “as safe as an airliner” – until the loss of CHALLENGER. By then it was deemed too late and too expensive to retrofit a truly effective escape system. This author only needed an escape system once – in 1961. But he is eternally grateful that it worked as advertised when he did need it.
Another shortcoming was the failure to demonstrate a fully automatic landing capability. It was a design requirement from the very beginning, supported by a Microwave Scanning Beam Landing System (MSBLS) and all the on-board computerization, but never actually proven. On all Shuttle landings the Commander has taken manual control (over the inputs to the computers, which always actually command the control surfaces) for the last minute or two prior to touchdown. Such landings have been beautiful to behold, but have also been costly in terms of the required training and proficiency levels. Surely a commander returning from a 2½ year mission to Mars would not be as “sharp” as one completing a two-week mission in Low Earth Orbit (LEO).
The Space Shuttle, however, was never intended to go deeper into space than LEO. At roughly 200,000 pounds mass (just under 100 metric tonnes) in orbit, with a lot of that devoted to ascent (main engines and piping, external tank fittings and doors, etc.) or entry and landing (aerodynamic controls, wings, wheels, etc.) it was too massive to realistically send to lunar orbit (and back). Additionally, the higher velocity returning from the moon compared to deorbit from LEO, would have required the Shuttle TPS to dissipate about 40% more energy – which it would not be able to do without major redesign and refurbishment. Consequently, America’s desire to push farther out into space – to asteroids, the moons of Mars, and eventually, to the surface of Mars itself, requires another vehicle – another “system.”
American culture holds that government should only do those things that cannot be accomplished by free enterprise. We have reached a point in the maturity of space technology where the private sector possesses the capability to build and operate launch vehicles, cargo delivery (to the ISS) systems, and even human transportation systems. As examples of novel cargo delivery systems, note the existence of the European Ariane Transport Vehicle (ATV) and the Japanese H-II Transfer Vehicle (HTV). The Space-X Falcon 9 + Dragon cargo module is expected to fly later this (2011) year. There have been attempts to field a human transportation system in the past, but all have had the specter of asymmetric competition from the Space Shuttle, thereby dampening prospective investor’s enthusiasm. If nothing else, the retirement of the Shuttle will remove this impediment.
While the launch and reentry stresses on its crew were constrained to low levels to enable the “average man” to fly into space, and John Glenn at age 76 flew as a mission specialist, it did not really open the door to private space flight or “space tourism.” NASA’s restrictive policies forced interested individuals to arrange flights aboard Russian SOYUZ vehicles. Seven different individuals have made such flights, to the ISS, and have behaved and performed quite respectably.
The CONSTELLATION Program was, in spite of its flaws, presented as a complete system for return to the moon. The principal surviving element from this program is the ORION crew module, now dubbed the Multi-Purpose Crew Vehicle. It will enable human missions beyond LEO, but can be pressed into service to & from the ISS if desired. Its first unmanned test flight is planned in 2013, but could be accelerated in deemed appropriate. One of the recommendations (Paragraph 3.1) from the “Second Augustine Commission” (Seeking a Human Spaceflight Program Worthy of a Great Nation (2009)) was that the United States should develop broad capabilities first, and select the specific destinations later. It is down this path that the United States is now proceeding. In the meantime we (collectively with our partners) have completed construction of the ISS. Now with six crew members permanently on board it is time to concentrate on research and reap the returns on our investment while the next generation of crew transportation/exploration vehicles completes development.