How much fuel can be saved for moon-earth missions and vice-versa? If we have a space station on moon similar to what we have what are the gains?
Sundaresan,
If you posit an orbiting station around the Earth then you automatically save about a tonne per person of entry capsule.
But.
And it's a big but, you still need to brake into a LEO - and without using aerocapture, that means fuel. So it's not at all clear that a 'returning to a space station' model has a smaller launch mass than a ballistic aerocapture return.
The only way to be sure is to grind through the numbers, using the rocket equation and some plausible stored fuel combinations.
If you have a station orbiting the moon, then trips back and forth to the surface are a simpler exercise to calculate. You've got the rocket equation, a choice of Isp, and go from there with some plausible vehicle dry masses.
I suspect all of the above has been done to death at least 40 years ago. The NASA technical report server is online at:
http://www.sti.nasa.gov/
Or find an old hand to chat to at the LPI in Houston each spring.
Being a launch vehicle configuration designer myself, I would run away from designing such a vehicle and leave the design work to a design genius or magician. Instinctively it makes me feel that I have to get a number much greater than one from a initial start of unity a value representing the normal launch vehicles which are generally designed.. Given a space station around the Earth and another around the moon would bring my enthusiasm back alive.
Dear Sundaresan, I am currently working on a L2 station with a fuel depot attached to it. I am planning on for crew of 2 in the orbit. I looked into pros and cons of putting a station in L2. We can save some mass by selecting the launch vehicles that can provide with excess Delta V to catch the L2 trajectory. Putting Fuel Depot in orbit has boil off issues and that might reduce the efficiency but boil off is less than that in LEO.
For to and fro from moon if we use Dragon spacecraft with trunk on Falcon Heavy for transferring the crew, we have excess Delta V of around 4km/s and do need extra propellant for catching L2 trajectory and Halo orbit. The propellant depot can be used to refill the returning propellant for Dragon or any other spacecraft being used. We save on carrying extra fuel for breaking in LEO by this way.
I would like to corrected if I am wrong somewhere since I am still learning about the stuff. Thanks
@Abhishek Jain
thanks for the response. Since you are already working related to such missions you would be covering finer details. I am having a basic question as to what will be a launch vehicle mass for two astronauts to land on the moon from the Earth. If the same exercise is done from the moon what the vehicle mass will be? T he same mission for to and fro from Earth to moon and back what the launch vehicle mass will be. You can choose any optimal path as L2 or otherwise.
I dont know if I understood your question correctly but I will try to answer whatever I got. To determine the mass of the launch vehicle one needs to know the mass of the spacecraft, logistics and propellant. Depending upon the dry mass of the launch and delta V involved mass of the propellant can be calculated using the rocket equation. In case of Earth- Moon a delta V of 6 km/s is required to land on the moon from LEO. With a choice of ISP and assuming the payload of 20mT an engine with an exhaust velocity of 4.5m/s, it needs around 15-20 mT of propellant from LEO to Moon. So the total vehicles mass from LEO will be 35-40 mT. similarly from moons surface the delta V to LEO is still 6 km/s but depending upon the mass of the space craft and supplies left the amount of propellant needed will reduce. for example if the mass lifting up the moon surface is 10 mT then the amount of propellant required is around 7-8 mT. so total space vehicle mass will be 17 -18 mT. These figures will change in different mission scenarios. This was a very basic example of calculating the mass for any mission. Hope I was able to answer a little bit of your query. Apologies for poor English.
@ Abhishek Jain
Thank you. When one starts the actual design exercise for a fixed payload mass, available propellants, feasible structural factors and then size a launch vehicle from earth and moon separately for a landing mass of two astronauts with space gear, and empty structure mass while landing; which in this case would be no less than 700kg; one can get a real feel.
From this assuming say three stages the launch mass with the ideal velocities you have assumed can be independently calculated.
Now when you are going to design a combined mission namely from Earth to moon and back the exercise becomes interesting. i hope in your spare time you can attempt this if you feel convinced. Any designer is happy only when a thing is practically viable. Building a launch vehicle is another thing.