Talk-Polywell.org

Fun thing will be when the rockets start taking off, refueling while in space, then landing with enough to take off again, making the ground the stop off point, not space.

kunkmiester wrote:Fun thing will be when the rockets start taking off, refueling while in space, then landing with enough to take off again, making the ground the stop off point, not space.

Never happen with chemical fuel. The delta V to come down from orbit would be the same as the delta V needed to reach orbit so It takes way to much propellent to land a full load of propellent. And staging would be a trick to pull off.

I suppose someone could calculate the Isp needed for even a modest mass ratio rocket to pull off the down and up trick though.

The point would be to switch from terrestrial fuel to space based fuel. The trajectory wouldn't change much--you need just enough lag time for a tanker to meet and transfer the fuel load. If the rocket has enough gas to go up then back down, it should work. Problem I just thought of though is that they're using super chilled fuel to get things to where they have the load to make these maneuvers. While it would mean lifting off with a partial fuel load, it might not work well to leave it sitting around on the ground getting warm while reloading the rocket.

kunkmiester wrote:Fun thing will be when the rockets start taking off, refueling while in space, then landing with enough to take off again, making the ground the stop off point, not space.

You could argue the we've been there, done that, in the manned Lunar landings.

As for not being able to do that with chemical fuels from LEO, well, yeah. But that's not what this forum is about, is it? If you're not thinking in terms of nuclear propulsion, you'll always be blocked from most of the potential of space.

The main thing I was seeing is you'd probably be saving a bit of fuel on lift-off, since you don't necessarily have a full rocket. You'd also have a price point savings, since the orbital fuel should be a bit cheaper to get despite transporting it to earth.

I've been wanting to see some math done on my rogue rocket ideas, though not sure how exactly to get that started.

It’s not, and never ever has been, about the cost of energy to get to orbit. Such arguments are flawed.

It is, because ISP drives so much of the design process, but it isn't, because until now expendable launch vehicles have had fuel as a small fraction of their cost-- but it is now because the Falcon 9 reusable is shrinking the cost of the hardware per flight.

By the time things get to the point where my thought is feasible (it may not ever actually be done for any number of reasons) the cost of fuel will probably be one of the larger costs of a flight.

According to Musk, the cost of the fuel in a first generation Falcon 9 was 200,000 USD. The newer F9 models are quiet a bit larger. Not sure exactly by how much volume has increased, but I would be confident saying that the cost of the fuel for an F9 launch is less than 500k USD.
Considering that a F9 launch (with a small enough payload for recovery) is currently about 62 million, the fuel (currently) makes less than 1% of the total launch cost. This relationship will probably start changing, once they start reusing their boosters more often. But there is a natural limit to how low the prices can go. With the current system, the booster makes about 3 quarters of the cost of the whole vehicle. The upper stage is 1 quarter. Add costs for range, launch operations and some profit margin, they may be able to reduce the launch cost by 50% with the Falcon9. So the fuel will still make only 2% of the total launch cost.

That would be great if that were to occur. But right now fuel costs are just a small fraction of the cost of a rocket even when you include the infrastructure necessary to super chill the fuel like the falcon nine rockets are using. The ideal solution to open up our solar system is paraphrasing as Tom L says"unless you're using nuclear rockets you're just playing around the space travel"

paperburn1 wrote:That would be great if that were to occur. But right now fuel costs are just a small fraction of the cost of a rocket even when you include the infrastructure necessary to super chill the fuel like the falcon nine rockets are using. The ideal solution to open up our solar system is paraphrasing as Tom L says"unless you're using nuclear rockets you're just playing around the space travel"

I agree. There is some hope it fusion powered rockets like the FDR proposed by MSNW LLC. That is only interesting once you are in orbit, though. Getting to LEO is what drives the cost.
If the DPF worked, we would even have a solution for launch (Miley et al had a paper about that).

Short of a breakthrough, even nuclear is dubious. None of the nuclear thermal designs (best ISP that has the thrust to actually lift off) right now have the ISP and thrust/weight needed to break the payload issue you're only doubling chemical's already low payload fraction, at least as I understand the math. Nuclear also gets into fallout issues--you can do plenty if you accept a certain amount of nuclear pollution, but if you want a clean rocket, it's not much better than chemical.

kunkmiester wrote:Short of a breakthrough, even nuclear is dubious. None of the nuclear thermal designs (best ISP that has the thrust to actually lift off) right now have the ISP and thrust/weight needed to break the payload issue you're only doubling chemical's already low payload fraction, at least as I understand the math. Nuclear also gets into fallout issues--you can do plenty if you accept a certain amount of nuclear pollution, but if you want a clean rocket, it's not much better than chemical.

Thats why I hope for a breakthrough in nuclear fusion. Would open a lot of possibilities.

I was looking at the launch schedules and it looks like SpaceX has rolled a bunch of stuff to the right. Maybe less busy for the rest of the year than I thought before.

Looks like they have made changes to accelerate the falcon heavy schedule .
that's why they reserved the three pads for next month....

SpaceX has shipped its Mars engine to Texas for tests

The Raptor is SpaceX's next generation of rocket engine. It may be as much as three times more powerful than the Merlin engines that power its Falcon 9 rocket and will also be used in the Falcon Heavy rocket that may fly in late 2016 or early 2017. The Raptor will power SpaceX's next generation of rocket after the Falcon Heavy, the so-called Mars Colonial Transporter.

http://arstechnica.com/science/2016/08/ ... for-tests/