I’m always happy to learn that NASA is conducting new technology demonstrations – and the recent success of an inflatable heat shield is no exception!
Congress has determined that NASA should follow the 1960s vision of space travel: you launch in a vehicle, you travel through space in that same vehicle, and you land in that vehicle. Sounds all nice and cozy, except that the last five minutes of your trip require a heat shield, which is massive – eating into the amount of food supplies, scientific instruments, and astronauts you can launch in the first place. Until the moment of re-entry, the heat shield is just dead weight, doing nothing and eating into the mission planners’ mass budgets. This whole architectural problem is one of the big reasons why I favor assembling interplanetary exploration vehicles in space and then taxiing up and down to those vehicles with capsules, instead of trying to take capsules to the Moon, asteroids, or Mars.
How about if your heat shield didn’t have such a huge mass? And how about if your spacecraft could stow it neatly away, so that its size and shape wasn’t a design driver of the launch vehicle or capsule shape? Some of those problems wouldn’t be so bad.
This is a big step towards opening up more flexibility for mission architects. I hope the technology finds its way onto some real missions in the near future!
I could not agree more. The idea inflatable heatshields and inhabitable living space are not new, but it seems that the inflatable heatshield finally comes to fruition. About getting heatshields on and off worlds, that is why we used a separate LM and CM/SM for Apollo:
Although we could build a capsule with less than a ton with an astronaught in it, in order to let the astronauts do science and return samples we needed a capsule with a mass of about 5 tons. This capsule needed an heatshield of about its own mass. We are up to 10 tons already. To return this capsule from Lunar Orbit to Tellus, we need its own mass in fuel. We are up to 20 tons. To get this off of Luna to Lunar Orbit, we need its own mass of everything so far in fuel which is 20 tons of fuel, which brings us upto 40 tons so far (the enginebells would have to endure a long continuos burn to get off of Luna, so it is better to make this a separate stage). To go from TransLunar Injection to Lunar Orbit and then from Lunar Orbit to the Lunar Surface, requires as much fuel as the total mass of everything else, which is 40 tons of fuel, which brings the mass up to 80 tons.
We halved the mass by using 2 spacecraft:
We have a 5-ton capsule, with a 5-ton ascent stage structurally built into it. we are up to 10 tons. We lower this from Lunar Orbit to Luna with a separate descentstage with landing gear built into it with 10 tons of fuel. The total mass of the spacecraft is only 20 tons. Notice the lack of an heatshield. This is the LM.
For entering and leaving Lunar Orbit, we have another spacecraft. It has a 5-ton capsule. For returning to Earth, it has a 5-ton heatshield. That brings the mass up to 10 tons. A stage with as much fuel as the total spacecraft so far, or 10 tons of fuel drives the spacecraft. The total mass of the spacecraft is 20 tons. This is the CM/SM.
By using 2 spacecraft instead of 1, we halved the mass of what we must send to Luna from 80 tons to 40 tons for each manned Lunar Mission. In light of this, in 1962, NASA decided to use 2 spacecraft for each Apollo for each Lunar mission. Rather than having to build a rocket capable of launching 100 tons of payload to TransLunar Injection, we only had to build a rocket capable of launching 50 tons of payload to TransLunar Injection.
Breaking up spacemissions into separate spacecraft, as you suggest, is a good idea.