The ISS has operated
on a fairly consistent model for orbital assembly that requires three major elements in order to function:
A minimum 20,000kg lift capacity, payload diameter of 4.15m in the launch system(including both Shuttle and Proton
A Robotic Manipulator System (RMS) for berthing modules
Extravehicular Activity (EVA) or spacewalking for completing connections
Russian space station
assembly (including ISS, Mir, and Star Modules for Salyut 7) have used automatic docking rather than RMS berthing. One should not downplay EVAs role in Russian space station assembly; as early as Salyut 7, cosmonauts were
installing additional panels to her solar wings by spacewalking.
The ISS has proven that
this model works for both logistics and assembly, although I think using a shuttle integrated logistics module that can be
unloaded from within the Shuttles bay (Spacehab and Spacelab) is more practical than modules that need to be berthed to the
station using RMS before loading and unloading (MPLM; Multi-Purpose Logistics Module.
Before examining the station assembly manifest, I thought that the MPLM was left on the station between shuttle trips,
as its design seemed to favor that purpose.) By using a fully reusable launch
system with low hardware costs, it should be possible to make this model much more cost effective than Option C. The bottom line is, that the ISS is actually too forward-looking and futuristic for current launch
If our first fully reusable
launch vehicle is much smaller than expendables like Ariane 5, Titan IV, and Proton, there may be a market for servicing satellites,
as the cost for servicing them might dip significantly below the cost of replacing them.
(For GSO satellites, a vehicle operating from a station might be required.) The
Space Shuttle rescued several satellites whose upper stages failed to ignite (a rare problem these days, and those that do
fail wind up in orbits unreachable by the shuttle or ones that decay too quickly.) It
might be possible that a future satellite launched at a cost of $300 million might need rescuing by a Bluestar(qv) that costs
$5 million to launch. Through repeated visits to the Hubble Space Telescope,
and servicing of other satellites, the Space Shuttle has proven the feasibility of orbital servicing.
The Space Shuttle has
taught us a lot about the vagaries of atmospheric entry. The wings went through
two structural revisions because aerodynamic force theories before the shuttle flew werent perfectly accurate. Plasma effects forced revisions on the elevons thermal protection (Columbia remained relatively
unmodified in this regard and, as of this writing, may yet prove to be the cause of her demise.) The Shuttle has proven that lifting entries followed by dead stick landings are relatively easy and safe. We also have experience from ASSET and X-23.
It should be fairly easy to develop entry lift and entry protection for the next generation of manned spacecraft using
our knowledge gained from the Space Shuttle.
Backup Recovery Modes
This lesson was taught
not by our successes but by our failures. During STS-33's break-up, the crew
cabin survived until it hit the water. Theoretically, all it needed was a parachute
system to soften the landing, and a couple of balloons to keep it afloat. On 6 December 1957, after the first Vanguard orbital
attempt exploded, the tiny satellite still worked after falling through t he fireball to the concrete.
The following quotes
from an introduction to a documentary on Challenger rammed backup recovery modes home enough for me to write specifically
KENT SHOCKNEK (KNBC anchor, Los Angeles): If the oxygen(sic)
packs were used, that means they survived the explosion.
JAY BARBREE (MSNBC science
reporter): But you can rest assured, they did not survive the impact.
More specifically, about
forty minutes into the documentary:
ROGER BOISJOLY (Former Morton Thiokol Engineer): The astronauts were alive.
The vehicle continued to climb and fell from some nine to twelve miles up. (Approx
45-60,000 feet. PAO stated immediately after the explosion, before he realized
it, that Challenger was at 9 nm altitude, so I think the apex is more like 65-75,000 feet.)
These conditions are
quite probably about the easiest conditions to execute a backup recovery from.
Backup Recovery Mode,
as I call it, is the building into the crew cabin the ability to survive a catastrophic failure of the rest of the vehicle. Launch escape is escaping the catastrophic disaster, and that's different. Backup Recovery Modes are also applicable in entry situations (although it likely would not have helped
Columbia.) Because the survival of backup recovery modules is passive,
no reaction system is needed. The challenge lays in packing enough systems into
the module and making the module itself tough enough to survive most likely catastrophes.
After surviving the catastrophe, the systems must then recognize the catastrophe and react quickly enough to
save the crew. Here are some ideas for a Backup Recovery Mode for an STS-like
Stabilization: pack the weight off-centre from the module's centre of figure to offset the centre of gravity. This will allow aerodynamic drag to orient the vehicle heavy end first.
Put in a passive wheel (perhaps adding this function to a nose landing gear wheel) on a moderate friction system with
an offset weight that will damp out oscillations in the vehicle's attitude. If
a landing gear wheel is used, the offset weight can be removed as part of its deployment sequence during normal operation. With passive stability, a backup recovery module doesn't need an attitude control
Thermal Protection: put the backup recovery module in the structure so that it is isolated from the brunt of explosive forces
and breakup debris for the first few seconds of the catastrophe, then have the module jettison the damaged structure. Assuming the underlying module did not suffer much damage, this should produce predictable
flight and thermal properties for the backup recovery module. This encapsulation
also protects the module's separate thermal protection system, a requirement for backup recovery from high altitudes and speeds.
Signal Capability: Nothing complicated, a radio, visual, and sonar locator beacon to
make the module easy to find by rescue forces should do fine. Just because
a BRM can survive catastrophic failure doesn't mean the crew can. It is likely,
even in the best cases of Backup Recovery, that the crew may suffer serious injuries, and search and rescue need to be able
to find them quickly.
sealing and floatation: If the module lands in water, it doesn't do the crew much good if it sinks. Landing bags are a good idea: if the module hits land, the landing bags can cushion the impact; if it hits
water, the landing bags keep it afloat.
the catastrophic: The reaction system needs to be able to accurately recognize a catastrophe, especially if a separate automatic
abort system is available (the system needs to answer do I abort, or do I do backup recovery?)
This is probably best done using multiple accelerometers, or reacting to massive simultaneous systems failure of a
kind that would indicate vehicle breakup or loss of control. If a launch escape
system is used, backup recovery mode should incorporate it into a common system. In
the Shuttle's case the best recognition is probably, "Hey, I'm not getting any power from any of the fuel cells, and the switch
positions say they're all turned on...that's weird, plus, my gimbals are all wacky."
and Rescue Standby: Let emergency (local police, fire and EMS) forces in the downrange know in advance when a mission is planned
to launch or reenter, and also how to recognize a backup recovery module, just in case.
This should also be put in the press kits for the missions. I wouldn't
be expecting them to line up ambulances and fire trucks under the ground track, but it would help them to, for example, know
that a report of falling debris might be from a spacecraft carrying toxic, hypergolic propellants, be able to tell the responder,
and then execute their contingency plans for finding the backup recovery module.