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My impression is that air launch will have plenty of niche uses but is not the best
path to Mars colonisation.
There is an advantage to air-launch toward orbit, but it is small for subsonic launch from a horizontal carrier. The effectiveness counts down from (1) very high speed at launch (low hypersonic or at least high supersonic), (2) angle close to 45 degrees at launch, and (3) high altitude (above 40,000 feet) at launch. The angle at launch is more important than you would think, because any vehicle that must pull up from horizontal, incurs enormous penalties due to an incorrect velocity direction (a vector addition problem), and to drag-due-to-lift (inherent physics of aerodynamic flight).
The original air-launched ASAT weapon launched from an F-15 doing about Mach 1 or even low supersonic, at a path angle upward very nearly 45 degrees. At altitudes above 20,000 feet. Near the top of its flight envelope (vicinity of 50,000 feet), the F-15 could not achieve path angles that steep. It's called "service ceiling", but the physics are actually quite fundamental. So it was more important to achieve angle than altitude. Speed was just limited to "around Mach 1" by the performance of the airplane, but shows up to first order, in the rocket equation that the weapon must satisfy.
I designed the "Minuteman" chase mission and "one-off" configuration for "Scout", that enabled the seeker on that ASAT weapon to actually work for the first time in a critical test. I did that way back in 1974. That mission flew in 1975, as depicted by the photo on the cover of Aviation Week magazine. We had the operational ASAT several years after that. Interesting work, if you are lucky enough to get it.
GW
Let's Go to Mars...Google on: Fast Track to Mars blogspot.com
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Louis,
Nobody here is suggesting that we're going to colonize Mars using repurposed miniature air-launched ICBMs. I'm suggesting that sending a single astronaut or pair of astronauts to the ISS aboard a space capsule large enough for 7 people is a waste of money. This is a cost reduction strategy to enable NASA to keep servicing ISS while spending more money on tech required to explore and colonize other worlds.
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I am not an aeronautical engineer. But I can see some significant advantages of small launchers over big ones.
1. A very small launcher could be air launched from a repurposed 747 or maybe something even smaller.
2. If we want to deliver 1000te of materials to LEO, then launching it 1te at a time using multiple small launchers every eight hours, say, allows scale economies that might not be achievable if we are launching 100te payloads once a month.
3. If electromagnetic launch assist is employed, then regular launches of very small payloads is much easier than larger mass launches that occur only occasionally, because the power requirements of a launch are proportional to mass launched and capital costs scale with peak power requirements. That means that a launcher capable accelerating 100te vehicles to 2kms will cost ten times more than a launcher capable of accelerating 10te vehicles, even if total payload delivered per year is the same. Electromagnetic launch works well for regular or continuous low mass launches.
Hypothetical scenario. We build an electromagnetic launcher capable of launching vehicles from Earth surface at a rate of 1 per second, at a launch speed of 2kms. Each vehicle is a cruise missile sized SSTO, reusable, weighs 1000kg and delivers 100kg payload to LEO. Assume a 50% efficient launcher. The power requirement works out to be 4GWe. We could power the launcher without energy storage using some 10x 400MWe combined cycle gas turbine power plants. Total capital cost of the power plants, would be about $4billion. Let's assume that the EM launcher is about the same,mso total capital cost is $8billion. That's an achievable investment.
If one payload is launched every second, total delivery to LEO would be a little over 3million tonnes per year. Let us assume amortisation over 20 years and a 5% interest on capital for the launcher cost and a $0.1/kWh cost for electric power. Launcher capital costs come to $133/tonne or $0.13/kg. Electricity cost is $1.11/kg delivered to orbit.
The launcher is a really cheap way of boosting small rocket payloads. But it really only works for small rockets launched in rapid succession. If we tried to boost rockets with takeoff weight of 100te to 2kms, say, the electric power requirements would be equivalent to the entire North American grid.
Small cruise missile sized rocket vehicles are also suitable for mass production. If we can build them for about the same cost as a cruise missile, then they would cost about $1million each.
Last edited by Calliban (2021-01-19 06:37:50)
"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."
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The US space program was started with Mercury which was a ICBM converted for a single man to go to orbit.
With todays materials it would be a much lighter mass rocket and would have more capability than its predecessors.
We did do a topic on the EML microwave launch system of KBD512 and from ground level it has some defined needs to be successful.
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