68
votes
Accepted
Why don't we know exactly where the Chinese rocket will fall?
If the orbital period is about 90 minutes, that means ±45 minutes error at predicting the moment of landing means randomizing that point all around the globe. At the moment the prediction error is ± ...
- 54.9k
58
votes
Could an astronaut safely shoot the Sun with a gun?
The Earth's orbital speed around the sun is about 30km/s. Firing a bullet from the vicinity of Earth's frame of motion (e.g. from low Earth orbit) to hit the sun would require cancelling out most of ...
- 167k
51
votes
Why are all trajectories in space a conic sections?
Not all trajectories in space are conic sections, only those that are a two body problem. One planet in orbit around a star is a two body problem. Only two body problems are solved by a conic section.
...
- 48.8k
42
votes
Could an astronaut safely shoot the Sun with a gun?
T-Rex with his tiny brain overlooks the Coriolis force. If the astronaut pointed the gun at the Sun and shot a bullet, it would miss spectacularly. The orbital motion of the Earth makes for a sideward ...
- 1,696
37
votes
Without the accident, would Apollo 13 still have been the farthest crewed mission from the Earth?
You've hit on a really interesting question. To answer this, I'm going to look at JPL Horizons, using the center of the Earth and the center of the Moon as the distances provided. I'm going to look at ...
- 121k
31
votes
Accepted
Is 678 km the new altitude record for a rocket shot "straight up" (vertical launch)?
New Horizons went into Earth parking orbit first, so it doesn't count.
For a suborbital direct ascent trajectory, some early lunar probes (USSR's Luna-1 for example) would hold this record. Otherwise, ...
29
votes
Accepted
Can we set up an orbiting transporter between Earth and the Moon?
This sort of spacecraft is known as a "cycler".
You hit on the problem with it: you have to match its trajectory/velocity exactly in order to dock with it, so if you can reach the cycler, you could ...
- 167k
29
votes
Accepted
Is this plot of deep space trajectories correct? Did most launch retrograde from Earth? Why do some change direction between planets?
The diagram you show is the digital version of a drawing by someone with an Etch-a-Sketch: completely inaccurate. The diagram below is accurate, showing Pioneer 10 & 11 and Voyager 1 & 2 ...
- 18.2k
25
votes
Accepted
In deep space missions, how much of the journey is pre-programmed and how much is "direct" control?
The journey to the destination is about always completely pre-planned. All the gravity assists, close fly-bys, and so on, are planned before launch - and often long before the probe design is ...
- 54.9k
25
votes
Accepted
Did any spacecraft ever use the Sun's gravity for acceleration?
It doesn't really work that way. We can use the Sun to change direction, but we need rocket thrust to increase speed with the msneuver.
To begin with, the closest stars (apart from the Sun) are not ...
- 8,445
25
votes
Why are all trajectories in space a conic sections?
The question of which force laws allow what kinds of orbits received considerable attention in classical mechanics, some of it very recent. The strongest result dates to 1873, when Joseph Bertrand ...
- 7,778
24
votes
Accepted
What is the reason for the Ariane 5 launcher with Intelsat 29e losing altitude?
Altitude drops like that are common when the orbital stage has a high-efficiency, low-thrust engine.
It takes a few minutes for the upper stage to bring the craft up to orbital speed. During that ...
- 167k
24
votes
Accepted
How much reentry speed did the Shuttles shed by doing a series of sharp turns?
It's a bit of a misconception that the shuttle used S-turns to slow down. To quote the Entry, TAEM, and Approach/Landing Guidance Workbook by the United Space Alliance:
The next time you hear ...
- 1,954
24
votes
Accepted
Why is Artemis 1 swinging well out of the plane of the moon's orbit on its return to Earth?
The return orbit has a high inclination to align with the planned Entry Interface (EI) target line shown in figure 4 from Trajectory Design Considerations for Exploration Mission 1.
Each short blue ...
- 17.5k
23
votes
Accepted
If I wanted to reconstruct an entire Apollo mission's crewed spacecraft trajectories, what are the key sources of historical data I'd look for?
To answer the question literally: you'd be looking for NASA Apollo Trajectory (NAT) data files.
The report Apollo Mission 11, Trajectory Reconstruction and Postflight Analysis Volume 1 (PDF) provides ...
- 14.1k
23
votes
Accepted
What did I see just before the ISS but on a different trajectory?
I found it.
It was NOSS 3-1, a satellite pair.
Found it through heavens above.
The pair also explains the apparent tumbling. However, it seemed much brighter than 4.1, but it‘s definitely it.
- 439
23
votes
Did any spacecraft ever use the Sun's gravity for acceleration?
The "gravitational" (slingshot) maneuvers space probes are performing are actually not so much about gravity. The gravity is method to "tie" temporarily these two bodies, but you could (purely ...
- 1,831
22
votes
Without the accident, would Apollo 13 still have been the farthest crewed mission from the Earth?
I believe the answer is yes, but just barely.
The distance from the Earth to the moon varies significantly over time, from 356,400 to 406,700 km. I plugged the dates of orbital entry and departure ...
- 167k
22
votes
“Parabolic”, suborbital and ballistic trajectories all follow elliptic paths. Is there a generic term for these trajectories?
All the analytical orbits I'm aware of are conic sections or conics, including parabolas, ellipses, and hyperbolas. This includes the truncated / terrain-intersecting trajectories you're using as ...
- 9,860
22
votes
How do the interferometers on the drag-free satellite LISA receive power without altering their geodesic trajectory?
Nothing is mounted on the proof mass. The proof mass is unpowered, ideally touches nothing, and is designed to be as featureless as possible. The ones used in Gravity Probe B are the most perfectly ...
- 7,778
21
votes
Accepted
Why don't we take the shortest route to Mars?
When a spacecraft is launched from Earth, it's moving counterclockwise across your diagram at a speed of 30 km/s (the same speed as Earth itself), plus a speed of 10-15 km/s in the direction of the ...
- 126k
21
votes
Accepted
Can the Falcon Heavy handle deep space missions?
SpaceX published numbers on their website near the bottom of the page.
I snapped an image to show here, since their formatting is prettier than I can do in Markdown.
You can see that it can do ...
- 79.3k
21
votes
Accepted
How does a space vehicle which carries Curiosity or Spirit rover reach a planet?
Movies are misleading.
Space is enormous, and almost entirely empty. Even our ”asteroid belt” is mostly empty space; we have flown several missions straight through the belt to the planets beyond ...
- 167k
20
votes
Accepted
How does one "dump" or deplete propellant without changing spacecraft attitude or trajectory?
In many cases, propellant is only dumped when the spacecraft’s mission is complete, so any minor changes to trajectory caused by the dump are unimportant.
If you must avoid any trajectory or attitude ...
- 167k
20
votes
Accepted
How to choose the best direction to leave Earth's sphere of influence?
Your intuition is quite correct.
The Hohmann transfer orbit is a bi-tangential orbit, so at the point where the spacecraft leaves Earth, it is travelling in parallel to us.
In the case of Mars, we ...
19
votes
Accepted
Has any space probe changed course (in a large way) over time?
So first of all, every space probe changes direction constantly due to the gravitational attraction of the Sun, and the planets and moons. For instance the Parker Solar probe orbits the Sun every few ...
- 19.3k
19
votes
Why are all trajectories in space a conic sections?
The existing answers here are either wrong (making it sound like the conic section orbits are easily deduced by simple algebra from the inverse square law of gravity) or overly extensive and technical ...
- 444
18
votes
Would it be possible to go beyond Jupiter without making any slingshot?
It is absolutely possible, just not advised. New Horizons was launched at Solar System Escape Velocity, meaning it could have visited anywhere beyond Earth without stopping. It did visit Jupiter, ...
- 121k
18
votes
Accepted
Traveling through the asteriod belt?
The asteroid belt isn't nearly as dense as popular media makes it out to be.
An answer from the Dawn Mission's FAQ, specifically "What is the average distance between individual asteroids? (6/13/10)",...
- 1,043
17
votes
Accepted
How to get true anomaly from time?
An exercise that was left unsolved from last year's class gives me this equation :
$$
t-t_{p} = \sqrt{\frac{a^3}{\mu}}*(\arcsin(X) - e*X)
$$
where :
$$
X = \frac{\sqrt{1-e^2}*\sin(v)}{1+e*\cos(v)...
- 73.2k
Only top scored, non community-wiki answers of a minimum length are eligible