50
votes
Do you need to burn fuel between gravity assists?
Yes, Trajectory Correction Maneuvers (TCMs) are always performed during cruise phases, whether before or after gravity assist flybys. This NASA tutorial serves as a good general reference.
One source ...
- 18.2k
48
votes
What are "Ohms burns" in the context of Scott Kelly, KSP, and the Space Shuttle?
That's a mistranscription of OMS Burn, or Orbital Maneuvering System burn. The OMS system is how the shuttle changed its orbital characteristics. You can read about it here. One, two or more might ...
- 1,221
48
votes
Accepted
Why is it so hard to build crewed rockets/spacecraft able to reach escape velocity?
Delta-V to LEO is about 10 km/s. From there to C3 (Earth escape) is another 3.2 km/s. It's just another 30% delta-V.
The problem is the Tyranny of the Rocket Equation. More delta-V means more fuel. ...
- 7,996
44
votes
When the ISS accelerates, do the astronauts feel it?
The answer to the question, "Do the astronauts feel the station moving?" is yes, definitely, but sometimes in an "indirect" fashion.
During Space Shuttle mission STS-109, when floating in my sleeping ...
- 4,175
43
votes
Accepted
How does a spacecraft know that it is in orbit?
The Juno spacecraft has no means to directly measure and compute that it is in orbit. It did not send any such confirmation message. All it sent was an FSK tone indicating that it had completed the ...
- 58.5k
39
votes
Accepted
Why is it most efficient to change orbit inclination while crossing the equator?
Why is it the most energy efficient to change orbit inclination while crossing the equator?
Specifically, it's most efficient to do a plane change at one of the two "nodes" where the origin ...
- 167k
36
votes
James Webb orbit insertion
How can JWST brake without turning around?
Answer: JWST does not.
From More Than You Wanted to Know About Webb’s Mid-Course Corrections!:
One interesting aspect of the Webb launch and the Mid-Course ...
- 9,542
34
votes
Why is it so hard to build crewed rockets/spacecraft able to reach escape velocity?
It's not hard, it's just expensive. We know exactly how to do it. Compare this to building computer processors with 1nm transistors, or making reliable self-driving cars. Those are both things that we ...
- 441
34
votes
When burns are made during inefficient parts of the orbit, where does the lost energy go?
After writing my comments, I started writing a new answer. That got long, so here's a shorter one.
The "energy of an orbit" may be poorly defined and depending on the definition, is not ...
- 10.6k
33
votes
Accepted
Do all artificial satellites have engines?
Most satellites do have a thruster system of some sort on board. Indeed, the lifespan of a satellite is often determined by how much fuel it can carry, because once it runs dry, it'll start to slip ...
- 2,734
29
votes
Why is it most efficient to change orbit inclination while crossing the equator?
A great aid to intuition is to remember one principle about orbit changes: if the engine is off, the orbiter always returns to same point one orbit later.
So for any orbit change, if you want to do ...
- 1,834
25
votes
Accepted
This ISS trash deployment looks more like 2 feet than 2 inches per second, was it too fast or are these articles incorrect?
What's the root cause of the disparity between what the article says and what's shown in the video?
There is no disparity. The article says you need a minimum velocity of two inches per second [bold ...
- 18k
25
votes
Are there any studies about "ping pong" cyclers between gas giants?
In a sense, this "ping pong" is what cycler orbits attempt to do, you are just overestimating the power of flybys.
To make the distance between Jupiter and Saturn in just 4 years (one way?), ...
23
votes
Accepted
Lowest delta-v maneuver to reverse the direction of a satellite in LEO?
Reversing direction is a special case of inclination- / plane-change.
Here's one way to find a better upper bound on the necessary delta-V for a 180 degree plane change:
Assume a 2-body system (i.e. ...
- 10.1k
23
votes
Accepted
Was SpaceX's launch of Formosat-5 more vertical than normal for any particular reason?
FORMOSAT-5 was deployed directly to a 720 km circular orbit, with only a single burn. In order to do a circular orbit so high, one has to have a more vertical ascent then would be typical. Basically, ...
- 121k
22
votes
Do all artificial satellites have engines?
Short answer: no.
most small satellites (like the cubesat you saw) don't have engines. Rocket engines are complex, and therefore expensive, and these small satellites are usually used in an effort to ...
- 126k
21
votes
Accepted
What prompted Lovell on Apollo 8 to announce "there is a Santa Claus"?
The first trans-Earth injection from the moon was a high-stakes maneuver; if the Apollo's SPS didn't fire, the crew would have been stuck very far from home. I always took "please be informed there is ...
- 167k
21
votes
How does a spacecraft know that it is in orbit?
Using attitude determination devices, (including doppler shift of radio signal from Earth), it can determine* its location and velocity relative to Jupiter, and from that data, and knowing Jupiter ...
- 54.9k
21
votes
Accepted
What is the smallest body in which a sling shot maneuver can be performed?
How small do you want to get? $F=G{Mm \over r^2}$ applies regardless of size. If you remove enough disturbances from other bodies you can get two neutrons to orbit a common barycenter on gravity alone ...
- 54.9k
21
votes
Accepted
What is the delta-v required to get a mass in Earth orbit into the sun using a SINGLE transfer?
Actually the answer is a bit more complex than "Earth orbits at 30 m/s, so you have to stop that velocity and drop in. Thus the delta-V is 30 km/s." The question states that you start from Earth orbit,...
- 18.2k
21
votes
Accepted
What are the benefits of supersynchronous transfer orbits?
This is a partially copied answer from this closely-related question:
The other answerer focuses on the straight-up dV savings which occur when you're launching from a very inclined launched site. I'm ...
- 10.6k
21
votes
Accepted
Why does the point of burn on an orbit stay at a constant altitude?
When calculating propulsive manoeuvres, we usually consider them as impulses. That is, happening in a very short time. This is usually a good enough model for chemical rocket engines which deplete ...
20
votes
Accepted
What happens to JWST after it runs out of propellant?
This Northrop Grumman video (starting at 09:31) illustrates JWST's orbit in a non-rotating (normal) frame. It's really in an orbit around the Sun about 1% farther ...
- 149k
19
votes
Accepted
What are "Ohms burns" in the context of Scott Kelly, KSP, and the Space Shuttle?
Since the questioner also asks "why are two needed" and the other answer didn't address that:
Early shuttle missions flew a "standard insertion" ascent. This required two burns of ...
- 178k
19
votes
Accepted
Delta-v to move from GEO to GEO
Theoretically, you can go anywhere in GEO for an arbitrarily small ∆v - you raise your apogee a little bit, which slows you down, wait until you've phased to your destination latitude, then re-...
- 167k
19
votes
What kind of mission objective would make a parabolic escape trajectory desirable?
Why zero excess velocity? Well, with almost zero excess velocity you can stay near Earth, but not too near. For example, the Spitzer space telescope did this to communicate with Earth while avoiding ...
- 11.5k
19
votes
Accepted
What is the equation that relates delta v of a rocket to time taken to complete an orbit?
There is actually no relationship between the two. In a simple 2-body problem, each orbit starts and ends in the same place with the same velocity vector. The "delta" in "delta-v" ...
- 17.7k
18
votes
How do orbital boosts affect the structural integrity of the ISS?
Yes. It is considered (sorry I don't know exactly how much, but probably a LOT - they track the torque on individual bolts during construction for example). They had an accident a while ago where a ...
- 4,585
18
votes
When burns are made during inefficient parts of the orbit, where does the lost energy go?
The sum of all mechanical energy will be the same after your ideal burns. The difference will be that the portion given to your exhaust will be greater for higher burns.
For a burn farther away from ...
- 6,667
18
votes
Accepted
During orbital rendezvous, at what distance and approach velocity does the transition from orbital mechanics to “boating around” occur?
Orbital mechanics always apply.
For shuttle the two different operational phases were referred to as Rendezvous Ops and Prox Ops
The breakpoint between the two was defined in the Space Shuttle Flight ...
- 178k
Only top scored, non community-wiki answers of a minimum length are eligible