# Compute Impact Velocity Vector for Orbital Trajectory

• guss
In summary: I simulated the impact and found that the craft would enter a nearly circular orbit at impact and would travel at a speed of .3116 m/s.
guss
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.

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?

## 1. What is the impact velocity vector for orbital trajectory?

The impact velocity vector for orbital trajectory is the velocity at which an object approaches a target during its orbital motion. It includes both the magnitude and direction of the velocity, and is an important factor in determining the outcome of an orbital mission.

## 2. How do you compute the impact velocity vector for orbital trajectory?

The impact velocity vector for orbital trajectory can be computed using mathematical equations and calculations based on the initial velocity, gravitational forces, and other factors such as atmospheric drag. This can be done using specialized software or by hand using formulas and data from the orbital mission.

## 3. What is the significance of computing the impact velocity vector for orbital trajectory?

Computing the impact velocity vector for orbital trajectory is crucial for ensuring a successful orbital mission. It allows scientists to accurately predict the path and velocity of an object, and make necessary adjustments to ensure it reaches its target without any complications or collisions.

## 4. What factors can affect the impact velocity vector for orbital trajectory?

Several factors can affect the impact velocity vector for orbital trajectory, including the mass and speed of the object, gravitational forces, atmospheric conditions, and any external forces acting on the object. These must all be taken into account when computing the impact velocity vector.

## 5. Can the impact velocity vector for orbital trajectory be altered during the mission?

Yes, the impact velocity vector for orbital trajectory can be altered during the mission through various methods such as thrusting, aerobraking, and gravity assists. These maneuvers can change the magnitude and direction of the velocity to achieve the desired impact on the target.

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