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 ...
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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. ...
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  • 47.3k
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 ...
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  • 1,666
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 ...
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  • 119k
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, ...
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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 ...
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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 ...
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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 ...
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  • 52.7k
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 ...
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  • 7,630
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 ...
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  • 5,667
23 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 ...
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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 ...
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  • 12.4k
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.
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  • 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 ...
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  • 1,791
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 ...
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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 ...
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  • 76.7k
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 ...
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20 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 ...
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  • 122k
20 votes

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 ...
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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 ...
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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 ...
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19 votes
Accepted

How many burns did the Apollo 11 mission need?

According to the plan, an Apollo mission to the moon uses eleven-ish burns. Here are the expected maneuvers: Launch from earth. This you might count as three burns, since it requires all three ...
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  • 3,940
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 ...
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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 ...
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  • 446
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, ...
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  • 119k
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)",...
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  • 1,013
15 votes

Is 678 km the new altitude record for a rocket shot "straight up" (vertical launch)?

Not sure if this counts, but New Horizons was launched directly into an escape trajectory and did not enter orbit. It made it to Pluto and beyond. From Wikipedia: New Horizons was launched from ...
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  • 1,156
15 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)...
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  • 65.6k
15 votes

Traveling through the asteriod belt?

The asteroid belt is roughly 6 Astronomical Units wide, and so when it is drawn only 600 pixels wide with each asteroid a handful of pixels wide, you end up with each asteroid being five times bigger ...
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  • 148k
15 votes
Accepted

Does trajectory of an object orbiting a planet depend on the object's mass? (With hypothetical Apollo example)

Approximately, yes. The gross gravitational effects on the trajectories of the spacecraft and the other object will be the same. The force of gravity between two objects is proportional to the ...
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