Tuesday, August 2, 2011

End of an Era Need Not Be End of a Capability

Update 7-6-21 added below
This one appeared as a guest column in the Waco Tribune-Herald newspaper of Waco, Texas. It is not about exploration, but about useful and necessary infrastructure in Earth orbit.

The last shuttle flight is complete, the orbiters are headed for museums, and thousands are being laid off at Cape Canaveral and Mission Control. There is going to be a hiatus in America’s ability to launch its own astronauts that may continue for a few years.

Actually, I do believe the private companies like SpaceX will fill that void sooner rather than later. I also believe there will be a second, privately-owned, space station up there, very soon.

But, these private ventures, which build upon 50 years’ expertise, will require smaller teams on the ground at the Cape and in Mission Control. Except for local employment prospects, that’s a good thing, because it means spaceflight will become less expensive.

I predict that more than one commercial spacecraft will be flying soon, and that some of our familiar launch rockets will be updated and man-rated to launch them. That’s what NASA’s commercial spaceflight initiative was supposed to achieve, and it looks to me as if it is succeeding.

Here is what we will have: space capsules as taxis to orbit, space stations conducting research and business, and NASA looking outward beyond orbit with men for the first time in 40 years. But, something is missing from that picture!

Oh, yes, the “space repair truck” function of the space shuttle will be missing. Remember it?

It was the self-maneuvering shuttle with the adaptable human crew, that enormous cargo bay as a work area, and that manipulator arm, which repaired so many important satellites, most notably the Hubble Space Telescope.

In hindsight, having to launch that capability in every mission makes less sense than having two or three vehicles like that up there all the time. When you need one, send the crew and some thruster fuel up with one of the new space capsules: same results, far less expense.

All we need is a crew cabin, a space frame about the size of the shuttle cargo bay, that manipulator arm, some thrusters, and thruster fuel tanks.

These could be assembled in place by docking-together modules small enough to be launched by the rockets we already have. This is not a gigantic project, there is no new technology here, just a planned series of launches to regain a capability that we lost with Atlantis’s final landing.

It makes sense to have one in the highly-inclined orbit near or docked to the ISS, one in the more standard orbit eastward from the cape (the kind of orbit Hubble is in), and one in polar orbit to service those satellites. This may not be exploration, but it would certainly be helpful to what we are already doing in space.

There will always be satellites needing repair, and we already have one space station to repair, maintain, and upgrade. We might even use this capability to help build the new exploration vehicles.

I recommend this idea to NASA as something worthwhile and necessary. Maybe some of those laid-off workers could be re-hired to carry it out.

Update 7-6-2021:

An update to this idea takes advantage of vehicles that have since become available,  and also some suit and breathing gas technology that has been forgotten-to-death,  about which I have written some articles. 

Vehicles already available or available soon:

These include the Russian Soyuz crew and cargo vehicles,  the Spacex crew Dragon / Falcon-9 combination,  and fairly soon the Boeing Starliner / Atlas-5 combination.  There is also Falcon-Heavy and Ariane-5 for delivery of large cargoes to orbit.  The Sierra Nevada Dreamchaser spaceplane may also become available fairly soon,  as will the NASA Orion.

Suit and breathing gas technology:

The trend to ever-higher suit pressures has produced bulky and constraining space suits.  They need not be operated at that high a pressure.  There is no reason they could not be operated quite safely at significantly-lower pressures,  as detailed in Ref. 1.  We did it that way decades ago.  Why not do it again?

Given that truth,  the spacecraft transferring crew to the repair vehicle could transition from full-pressure synthetic air to a lower-pressure enhanced-oxygen mix,  while on the way to the repair vehicle.  As discussed in the reference,  this could be done with about the same fire risks as sea level Earthly air,  based on the chemical concentration of oxygen available to support combustion.  Yet,  the transition from this mix to a low-pressure pure-oxygen suit would require no pre-breathe time. 

Crews riding up and down in the crew transfer vehicle typically use survival-type pressure suits,  just in case cabin pressure is lost.  Such suits can be used for a short EVA to transfer elsewhere,  but are not suitable for doing any real EVA repair work,  as cooling capacity is usually absent or quite limited.  Physical protection against external hazards is also quite limited in these suits.

Since these repair missions are at most a few days,  there is little risk in human exposure to low-pressure enhanced-oxygen mixes.   Exposure to pure oxygen is limited to a few hours at a time,  that being about the longest duration we can expect of a real repair-work EVA. 

Longer term,  this is also quite the convenient scenario in which to experiment with MCP suit designs,  especially those done as vacuum-protective underwear,  with appropriate unpressurized mix-and-match outerwear for thermal,  mechanical,  and UV light protection.  See Refs. 2 and 3 and 4. 

Updated figure:

The updated figure shows essentially the same features as are in the original.  The changes explicitly show the visiting crew transfer spacecraft,  the EVA airlock,  and some redundancy to the propellant tankage and maneuvering engines.  Depending upon the visiting spacecraft,  both parts,  equipment, and supplies,  plus the refill propellants,  might be brought up,  if cargo capacity permits.  If not,  the refill operation might be a separate launch. 

I have shown a rough guess as to size,  based on the old space shuttle cargo bay,  and a rough guess for the maximum maneuver delta-vee.  The propellants should be storables,  to take advantage of refilling techniques already being used at the ISS.  They could be the new "green" propellant,  if an appropriate oxidizer is available.  Monopropellant performance would be too low.

Unchanged are the suggestions for how many such vehicles,  and where pre-positioned.  One should be at the ISS in its high-inclination orbit.  Another should be parked in a low-inclination eastward orbit,  to take care of a great many items,  including Hubble.  A third should be parked in a polar or near-polar orbit,  to take care of a great many items in orbits like that.

The fundamental design features are still:  (1) a shirtsleeve crew cabin in which to work,  (2) and EVA airlock,  (3) a manipulator arm (two may even be better),  (4) maneuver propulsion sufficient to reach the job site,  (5) easy refill of propellants and supplies,  and (6) docking capability to support many crew arrival vehicles.  The manipulator arm is required to achieve "docked" position control with the object to be repaired,  regardless of the forces from moving people and supplies.  It also is required to hold the astronauts in position as the apply forces doing their work. 


With Hubble having serious failures right now,  it is clear that we have lost this wonderful asset,  or will lose it soon,  if it cannot be "fixed" from the ground.  Once it fails,  there are but two responsible alternatives:  (1) de-orbit the thing to destruction over the ocean,  or (2) mount a repair mission and replace the failing over-age avionics.  It will be a few years,  not months,  before the Spacex cargo "Starship" design might be ready to undertake such a mission. 

We currently have no vehicle that could capture it and bring it home for repair,  or could dock with it and make repairs.  There is just not time (or budget) to pursue a massive program to repair it.  Yet Hubble really is worthy of repair:  the mirrors and corrective lenses are the kind of asset that could be useful for over a century,  as have been many ground-based telescopes.  It is the avionics and the camera equivalents that need replacing from time-to-time.


There is no need to pursue a long,  drawn-out program to come up with a vehicle that actually could make the necessary repairs,  nor is there available budget to support a big massive "typical" government program.  This has to be done fast,  and it has to be done relatively inexpensively.  It makes sense to use existing assets to the maximum extent possible. 

I suggest these approaches:  (1) use an existing craft (such as a Cygnus cargo vessel) to be the basic hull of the crew cabin of the depicted vehicle,  (2) use the same manipulator arm that was used on the shuttle and is being used at ISS,  (3) use the same tankage,  propellants,  and engines that were the space shuttle's orbital maneuvering system,  and (4) use the same atmosphere hardware that is used on the ISS,  but with a reduced-pressure,  enhanced-oxygen mix (about 6.2 psia of 45% oxygen diluted with nitrogen).  (5) The airlock can be the same as one of the ISS airlock modules.  (6) Use the refilling connections currently used at ISS with Soyuz tankers.  (7) Pure oxygen space suits can be operated at or slightly under 3 psia (2.8 to 2.9 psia nominal,  with a safe-enough leakdown to 2.5 psia).

Only the truss connecting them need be custom-built,  and trusses are not complicated!  Speed and rapid results are essential,  and budgets must be modest.  This is not (repeat NOT) the usual NASA program!  This cannot be (repeat CANNOT BE) the usual corporate welfare program for "old space".  One or more of the "new space" contractors should do this!


1. 16 March 2018,  "Suit and Habitat Atmospheres 2018"  [analysis of in-lung wet oxygen partial pressures and oxygen chemical concentrations to address supple space suits,  adequate oxygenation,  elimination of pre-breathe times,  and fire dangers no worse than in Earthly sea level air]

2. 23 November 2017,  "A Better Version of the MCP Space Suit?"  [adding tensioning inflatable capstans to the elastic compression garment concept to create an MCP space suit that is easier to doff and don]

3. 15 February 2016,  "Suits and Atmospheres for Space"  [definition of adequate wet in-lung oxygen partial pressure for any space suit,  at reduced suit pressures,  plus illustrations of suits over time,  including MCP designs]

4. 11 February 2014,  "On Orbit Repair and Assembly Facility"  [an earlier article on a potential application of low-pressure oxygen breathing,  MCP space suits,  into an on-orbit facility for working in a vacuum environment protected from bright sunshine;  this facility is more of a repair base than a mobile repair truck]


Updated Figure

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