-2
$\begingroup$

Trying to work out a rough time estimate for an ASAT rocket to reach GEO height?

$\endgroup$
22
  • 1
    $\begingroup$ As far as I know, there are none at present, and nothing very similar either, so you'd probably have to do the design yourself. $\endgroup$ Jan 12 '16 at 5:08
  • $\begingroup$ I'm trying to work out the effect on travel time if rocket is fired directly at target rather than needing to enter a stable orbit. It takes hours for a satellite to reach GEO but if a direct ascent is made does that cut it drastically? - to tens of minutes? or is it still hours? $\endgroup$
    – Matt
    Jan 12 '16 at 5:26
  • $\begingroup$ Assuming you have a rocket that leaves you moving at about 10 km/s practically vertical by the time you are at an altitude of 100 km, you'll coast the rest of the way to GEO in about 6 hours. $\endgroup$ Jan 12 '16 at 6:25
  • $\begingroup$ Note my numbers are roughly pulled out of the air since you aren't giving us enough details to properly answer the question! $\endgroup$ Jan 12 '16 at 6:42
  • 1
    $\begingroup$ @Matt, you will not be traveling at 10 km/s all the way there, you are starting at that speed and gravity will slow you to a stop just at the point you reach GEO (and then fall back down if you don't have a collision). Just imagine it like you are tossing a ball into the air, it starts with some speed and slows down until reaching the peak and falling back down. Accelerating under propulsive action the entire flight would be a different story, but that is unrealistic in terms of your question and the apparent scope of your work. $\endgroup$ Jan 13 '16 at 3:40
3
$\begingroup$

To just intercept the orbit, but not remain there, you can travel at any speed above that required for the Hohmann transfer.

In other words your travel time can be reduced to as short as you wish, provided you have the fuel and acceleration available.

If you can't handle the maths, you could try some trial-and-error simulations with Orbiter for example (just look at the time needed to rise to the altitude you want).

Out of interest (not really an answer), there is a calculator though it only gives the fuel and delta-vee requirements for the Hohmann transfer orbit, not the transfer time. Also it does not do any calculations for the higher energy case you require.

$\endgroup$
2
  • 1
    $\begingroup$ "In other words your travel time can be reduced to as short as you wish, provided you have the fuel and acceleration available." Thanks for that @Andy but isn't there a limit to how much fuel you can carry because of the weight? $\endgroup$
    – Matt
    Jan 12 '16 at 23:16
  • $\begingroup$ Realistically, you cannot simply accelerate as fast as you want. We can talk about exotic warp drives or just ignore size and cost and pretend we can have a giant ASAT vehicle, but for sensible case studies the most you can expect is a high $Delta v$ manoeuvre sending you into a highly elliptic orbit that sends you to GEO altitude. Someone should consider how fast we could accelerate a Delta IV or Falcon 9 (or maybe even a Saturn V) with no payload. $\endgroup$ Jan 13 '16 at 3:46

Not the answer you're looking for? Browse other questions tagged or ask your own question.