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Posts Tagged ‘Space Station’

Wings or ‘chutes?

When you come to end of your journey, do you want to:

1) Roll to a stop on a runway, then climb down some steps and wait for a minibus to take you to the ‘terminal’.

or

2) Fall into the ocean, don a life-jacket, and wait to be rescued.

These appear to be the two modes that will be available to astronauts (professionals and ‘passengers’) in a few years. Granted, there may be some variation, but it will still be a choice of falling under parachutes, or gliding to a runway landing. Each has it’s pros and cons, but I suspect only one has a long-term future, at least for manned flights.

SpaceX's Dragon

SpaceX's Dragon

Now I’m no trained astronaut or engineer, but this is how I see it; feel free to comment.

Capsule landing:

Pros:

  • Simpler, cheaper design
  • Naturally stable re-entry, low re-entry risk
  • Less crew training required for re-entry and landing

Cons:

  • Limited cross-range, fewer re-entry opportunities
  • Possibly more expensive to refurbish for next flight (dunked in salt-water)
  • Requires more substantial recovery assets, especially for water landings
  • Additional sub-systems required for land landing (air cushion / landing rockets)

Spaceplane landing:

Pros:

  • Good cross-range, frequent return opportunities
  • May return to launch site, easier turn-around
  • Minimal recovery assets required
  • Easier to re-use (ignoring TPS for now)

Cons:

  • Re-entry control critical
  • More advanced training required for pilots (but they won’t mind!)
  • More complex and expensive
  • Probably lower payload fraction (it has to carry it’s wings into orbit)

There’s probably plenty more, but that’s how I understand it in a nutshell. But these are only the technical considerations.

SpaceDev Dreamchaser

SpaceDev Dreamchaser

Non-technical considerations for the two types of craft may be a little harder to quantify, but we’ll try it anyway:

Assume a high flight frequency. Satellites are being regularly serviced, the ISS is being resupplied, a number of Bigelow stations are continuously occupied as science stations and hotels. There are even tours to Lunar orbit (and maybe the surface?). Supporting this infrastructure are pure cargo launches, manned mini-sat deployments, and frequent tanker launches to refuel the various propellant depots. The manned spacecraft are being turned around quite quickly and re-used. Customers wishing to fly to LEO have their choice of vehicle to ride in…

Orbital's lifting body spaceplane

Orbital's lifting body spaceplane

Today, with the possible exception of the space tourists flown in the space Soyuz seats, astronauts are professionals, trained in the operation of their craft. Comfort, and other details like recovery method and convenience are relatively unimportant. When the scenario described previously arrives, however, most passengers on the spacecraft will be relatively untrained, and things like convenience and comfort will become more significant considerations.

Why would a passenger, wanting to fly to a LEO hotel and back, want to splashdown into the ocean, rather than land at an airport? Sure, there will be a few that want the ‘Apollo Experience’ but I doubt that will be a way to build a business long-term! As I see it, this is a big win for spaceplanes.

Boeing crew module

Boeing crew module

To over-use the airline analogy:

Imagine two airlines, flying say, Los Angeles to Auckland. On one, upon reaching it’s destination, the aircraft deploys parachutes and drops into Auckland harbour. Passengers fit their life-jackets, and are taken onto a boat, which then returns them to shore. They’ve arrived! Now I’m sure if this were the only option, it would indeed be popular, but would probably scare off some potential customers.

The other airline flies directly to the airport and lands in the conventional manner. It can’t carry quite as many passengers, due to the weight of the landing gear and all, but it is far more popular with passengers, and the total trip time is substantially reduced. The landing is a lot more relaxed, as the passengers don’t have to deal with emergency equipment (life-jackets), and none will become sea-sick.

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Clearly, for cargo flights, the capsule is probably going to be hard to beat for awhile, and the non-technical issues become largely irrelevant in this case.

This isn’t to say that capsules for crew launch are a bad idea. Far from it! The spaceplanes are still stuck on the drawing board, but the Dragon capsule has already flown (unmanned), and will probably be the first to carry paying passengers. That’s a good thing. But once the spaceplanes begin operating, I suspect a substantial segment of the market will shift away from the capsules for good.