Compute Impact Velocity Vector for Orbital Trajectory

Click For Summary
SUMMARY

The discussion focuses on calculating the impact velocity vector of a craft in orbit at a height of 50 km above a planetary body, specifically addressing the effects of forces acting against its motion. The key methods proposed include deriving parameters of a new Kepler orbit for short-duration forces and employing numerical simulations for longer-duration forces. A simulation conducted by a participant yielded an impact speed of 0.3116 m/s for a 1.3 kg cubesat under a force of 0.0001 N, demonstrating the complexities of orbital mechanics at low altitudes where air drag is significant. The conversation also raises questions about the role of air drag and thruster forces in such scenarios.

PREREQUISITES
  • Understanding of orbital mechanics and Kepler orbits
  • Familiarity with numerical simulation techniques
  • Knowledge of forces acting on objects in low-altitude orbits
  • Basic principles of air drag and its effects on spacecraft
NEXT STEPS
  • Research numerical simulation methods for orbital mechanics
  • Learn about Kepler's laws of planetary motion and their applications
  • Explore the effects of air drag on spacecraft at low altitudes
  • Investigate thruster dynamics and their role in orbital maneuvers
USEFUL FOR

Aerospace engineers, orbital mechanics researchers, and students studying spacecraft dynamics will benefit from this discussion, particularly those interested in impact velocity calculations and the effects of atmospheric drag on low-altitude orbits.

guss
Messages
246
Reaction score
0
Let's say a craft is in an orbit at a height h above a planet or moon. A force acts directly against the craft's direction of motion so as the force vector is always parallel to the surface of the central body. So, the craft will slowly decelerate and impact the surface. What would be the best way to compute the velocity vector upon impact? I don't have much experience at all with orbital trajectories, and it seems like an interesting question with simple parameters.
 
Physics news on Phys.org
If the force acts for a short time: Calculate the position+velocity afterwards, derive parameters of a new Kepler orbit, evaluate this at the radius of the planet/moon.
If the force is significant and acts in a complicated way for a longer time: Numerical simulation?
If the force is like air drag and small everywhere and the initial orbit is roughly circular: Assume a nearly circular orbit at impact, calculate the corresponding speed.
 
I wanted a more exact result for that third option, and I couldn't derive a formula, so I did a simulation. It was actually much easier than I thought it was going to be, pretty cool as well. I got an impact speed of .3116 m/s in the straight down direction. Craft mass = 1.3kg (cubesat), F = .0001 N in the direction opposite of velocity, starting from 50km orbit. Very strange to thing about an object coming in for landing this way, nearly in orbit extremely close to the surface.
 
In 50km, there is nothing which I would call orbit, there is too much air drag.
 
mfb said:
In 50km, there is nothing which I would call orbit, there is too much air drag.
The moon is a vacuum for all practical purposes, especially at 50km altitude.
 
But how do you get air drag there? Or do you provide that force via thrusters?
 

Similar threads

  • · Replies 10 ·
Replies
10
Views
2K
Replies
7
Views
2K
  • · Replies 11 ·
Replies
11
Views
2K
  • · Replies 19 ·
Replies
19
Views
2K
  • · Replies 17 ·
Replies
17
Views
2K
Replies
3
Views
2K
  • · Replies 6 ·
Replies
6
Views
3K
  • · Replies 51 ·
2
Replies
51
Views
6K
  • · Replies 10 ·
Replies
10
Views
2K
  • · Replies 1 ·
Replies
1
Views
3K