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Rockets have very high mass ratios. A fully fueled rocket is by mass almost all propellant. This is counterintuitive, other vehicles do not have that. Rockets a
by Gravityloss 6y ago
Rockets have very high mass ratios. A fully fueled rocket is by mass almost all propellant. This is counterintuitive, other vehicles do not have that. Rockets also have very high thrust to weight ratios.
One of the effects is that flying an almost-empty rocket is really easy. When landing, the Falcon 9 first stage actually has too much thrust to even hover stably with one ninth of engines running and that at only partial thrust.
So an empty rocket flying doesn't produce nearly as much noise or pressure waves. So, you could do it like this:
1. The light, almost unfueled rocket stands at airfield
2. People board the light rocket
3. The light rocket flies a short hop to an oil rig (20 km or so). Only one rocket engine needed for takeoff and landing.
4. The light almost empty rocket is fully fueled at the oil rig. It becomes a heavy fully fueled rocket. People stay inside.
5. Heavy fully fueled rocket takes off with all engines blasting with massive noise.
6. Most propellant is expended during acceleration. Heavy fully fueled rocket becomes light almost empty rocket.
7. The light almost empty rocket lands at destination airport with one engine.
8. People offboard
9. Goto 1.
- deleted 6y ago[deleted]
- nwah1 6y agoSeems more practical to use conventional transport to go to and from the rig, such as a helicopter. A crash with a rocket is both more likely and more devastating, and thus should happen away from population centers. Even if the return trip is less noisy. Also rockets pollute, which is another reason to keep them far away from people.
- inetknght 6y ago> Also rockets pollute, which is another reason to keep them far away from people. Some rocket engines use oxygen & hydrogen fuels which, after combustion, turn into water. I'm not sure I'd count water as pollution.
- Azrael3000 6y agoThe last point you make is only partially true. The Starship is using Methane and Oxygen and produces mostly CO2 and Water as output. Since they plan to produce propellant using the Sabatier process using renewable energy you get a nearly closed cycle. There's a fantastic video by EverydayAstronaut on Youtube about this topic.
- penagwin 6y ago> Also rockets pollute, which is another reason to keep them far away from people. The falcon rocket's use RP-1 which is kerosene, so the exhaust is just H20, and C02 - Granted C02 isn't great, but it isn't too toxic.
- mulmen 6y agoHow is this better than using a fast ferry or aircraft? Those have the benefit of being able to pick people up and drop them off from multiple points.
- jessriedel 6y agoYes. And it also means the passengers don't have to wait around for the rocket to fuel up on the platform. I think that takes at least an hour or so?
- Gravityloss 6y agoThe advantages are that you don't need to offboard and onboard, and you don't need personnel facilities at the refueling stop. Also fueling doesn't need to take an hour. The rocket consumes its fuel in minutes, fueling could be as fast.
- mulmen 6y agoThe fuel pumps are literally powered by the rocket and use high pressure tanks to prevent vacuums from forming in the tanks. How do you plan on achieving that on the pad?
- Gravityloss 6y agoIt's just engineering. It's much easier than the turbopumps on the rocket. The rocket pumps have a much harder job than these refueling pumps, since the rocket's pumps have to raise the pressure to higher than the engine chamber pressure, so in Raptor that would be about three hundred bars (4500 psi). No such issue in tanking as the rocket tank pressure is low. You can also just use electrical pumps with no weight or size constraints, since it's not flight hardware. Large scale LNG pumping solutions at least are off the shelf items for LNG tanker ships. There also exist solutions for what to do with the gases in the LNG tank when it's filled. Oxygen tank contents you can of course just vent to the atmosphere. Falcon 9 first stage flight lasts 2 minutes and 34 seconds. Tanks go from full to empty. [1] You could design the refueling operation to be ten minutes if it provided some benefit to you. 1: https://spaceflightnow.com/2021/01/07/falcon-9-launch-timeline-with-turksat-5a/ https://spaceflightnow.com/2021/01/07/falcon-9-launch-timeli... There are other reasons though why flying a lot of people routinely won't be a thing.