• Question: How would you map out where the refuelling points are? And how would you know you would not have run out of fuel by then?

    Asked by ThomasP to Naziyah, Namrah, John, Joanna, Hester, Gosia, Ed, Adriana on 9 Mar 2021.
    • Photo: Namrah Habib

      Namrah Habib answered on 9 Mar 2021:

      Hi Thomas! I hope I am understanding your question correctly. When a spacecraft launches from Earth it needs to take all the fuel it needs for its mission from Earth. Currently, we don’t have any refuelling stations in space but there have been discussions of creating space based fuelling stations but I don’t know if that is something that will come to be. Presently, if a spacecraft needs to go to Mars and back, it needs to be able to carry all the fuel required to get to Mars and back.

      In space, there isn’t really friction, so a spacecraft will travel at a constant velocity through space. I believe most spacecraft only use fuel to fix their trajectory so they can stay on the path to their destination, or to rotate so they can communicate with Earth. Many spacecraft don’t even use liquid fuel to orient themselves and rotate!

      Satellites in low Earth orbit do actually experience a drag force from Earth’s atmosphere so these satellites actually do lose some of their velocity and can fall a bit towards Earth. To counter this and prevent the satellites falling all the way back to Earth, many satellites perform “thruster burns” to get back up to their orbital altitude and velocity.

    • Photo: Hester Baird

      Hester Baird answered on 9 Mar 2021:

      As Namrah says, in general spacecraft must carry all the fuel they need for the full extent of the mission. However, there are some projects now to launch Mission Extension Vehicles (MEVs) which are a type of spacecraft that is sent up to space, and can dock with another spacecraft already in orbit around Earth to provide it with more propulsion/fuel, which allows the mission to carry on for longer.

    • Photo: Joanna O'Rourke

      Joanna O'Rourke answered on 10 Mar 2021:

      As to figuring out the amount of fuel you need, that’s part of the design work you do at the beginning! You decide how long you want your mission to run, you need to count up all the manoeuvres you’ll need to do that will use fuel, and generally you’ll add a big margin to the number in case you got something wrong. At the beginning of a project, when your mission isn’t generally well defined in terms of what it weighs, then you’ll add assume an extra 25% for example, or assume that you’ll do twice the number of manoeuvres you think you’ll have. And then later on, when you’re more sure of what the satellite will do and weigh, you’ll reduce it.

    • Photo: Adriana D'Souza

      Adriana D'Souza answered on 12 Mar 2021:

      Great question especially when you think of long car journeys and various fuel station along the way. Airplanes refuel at airports as you may know but in space as the other colleagues mentioned we plan for the full mission from the start as there are no refueling stations in space :).