# All Questions

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9 votes
3 answers
2k views

### How to calculate the planets and moons beyond Newtons's gravitational force?

The question Calculating the planets and moons based on Newtons's gravitational force was pretty much answered with two items: Use a reasonable ODE solver; at least RK4 (the classic Runge-Kutta ...
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13 votes
2 answers
5k views

### How to calculate data rate of Voyager 1?

I've read the following passage in the answer to the Quora question How can Voyager send a signal strong enough for us to receive, in spite of its enormous distance from us? And how can it have the ...
• 133
17 votes
2 answers
2k views

### Is this what station keeping maneuvers look like, or just glitches in data? (SOHO via Horizons)

I've been enjoying the JPL Horizons web interface and after I discovered the incredibly extensive database associated with SOHO (Solar and Heliospheric Observatory, also see sohowww.nascom.nasa.gov) ...
• 148k
37 votes
4 answers
15k views

### Effect of atmospheric drag on rocket launches and benefits of high altitude launch sites

What is the approximate influence of atmospheric drag on the cost of rocket launches? Is it beneficial to have launch sites located at higher altitudes? Cape Canaveral is at sea level, but I've ...
• 1,645
87 votes
6 answers
16k views

### How much bigger could Earth be, before rockets wouldn't work?

hint: Apparently the Tsiolkovsky rocket equation does not actually say that you can launch a conventional rocket into orbit around an arbitrarily large and massive body. I'm looking for a number ...
• 148k
14 votes
3 answers
6k views

### How to best think of the State Transition Matrix, and how to use it to find periodic Halo orbits?

I'll state my mathematical question about the state propagation and state transition matrices first, then show you a simple problem for which I would like to use these concepts to generate a densely ...
• 148k
12 votes
3 answers
2k views

### What would a "Kármán plane" look like, a bird, or a plane?

If I understand correctly (which I might not), the Kármán line is roughly the altitude where a "Kármán plane's" upward lift force at the orbital velocity for that altitude would be equal in magnitude ...
• 148k
5 votes
2 answers
1k views

### How do SDP4's "Deep space" corrections to SGP4 account for the Sun's and Moon's gravity?

The Simplified Perturbations model SGP4 is used to calculate Earth satellite state vectors (position and velocity) using standard ephemeris data encoded as TLEs (Two Line Elements). According to ...
• 148k
15 votes
1 answer
16k views

### What is a near rectilinear halo orbit?

A proposed option for the lunar orbit of a Lunar Orbital Platform-Gateway (formerly known as Deep Space Gateway) is a near rectilinear halo orbit, or NRHO. This excellent answer discusses the ...
• 148k
11 votes
1 answer
6k views

### Why is a near rectilinear halo orbit proposed for LOP-G (formerly known as Deep Space Gateway?)

Why is a near rectilinear halo orbit a good place for a Lunar Orbital Platform-Gateway (formerly known as Deep Space Gateway)? Are there specific logistical and orbital-mechanical advantages over ...
• 148k
17 votes
1 answer
6k views

### What happens to JWST after it runs out of propellant?

JWST will be orbiting L2 which is unstable equilibrium thus will require propellant for station keeping. JWST will carry propellant for 5-10 years. What will happen once it runs out of propellant? ...
23 votes
4 answers
8k views

### Starman/Roadster in a=1.795 AU orbit, now what's the method to this madness?

The question SpaceX's 4,425 satellite constellation - what's the method to the madness? received an excellent answer explaining the rationality behind the madness plan. Elon Musk's tweet (spotted ...
• 148k
17 votes
4 answers
3k views

### Are some Halo Orbits actually Stable? (stable orbits about unstable Lagrange points)

update: some more sources; the broken site spacecraftforall.com/a-new-orbit used to have an interactive simulation, here's an old screen shot: Hat tip to @NgPh for finding this Space College page ...
• 148k
11 votes
1 answer
955 views

### What sort of orbital elements are used to describe halo orbits?

For standard orbits we can use Keplerian elements, TLE, or other similar. These don't make much sense for Halo orbits, which are not around a central body, but around a Lagrangian point, and follow an ...
• 52.4k
4 votes
2 answers
324 views

### Quantitatively, why will optical communication be better than X-band for deep-space communications?

In a question about communicating with Voyager, an answer asserts: [70 meter dish antennas deployed in space] just isn't done, and it probably won't be, since optical communication is definitely ...
• 973
32 votes
7 answers
14k views

### How could a 90 m/s delta-v be enough to commit the space shuttle to landing?

Wikipedia claims (although with no citation) that in order to make the space shuttle land, an initial powered delta-v of 322 km/h was applied in orbit, retrograde to the shuttle's orbit. 322 km/h is ...
• 7,186
29 votes
7 answers
4k views

### What technological hurdles prevent the development of a space gun?

Ever since Jules Verne wrote "From the Earth to the Moon" space guns have long been proposed as a method of launching objects into space. And for non-human, non-fragile payloads they make sense as the ...
• 3,009
21 votes
2 answers
2k views

### Going from LEO to lunar using only low-thrust ion propulsion - can it be done?

@SF.'s question What are the parameters of the new Iodine electrical rocket engine developed by RSC Energia? links to the short RT article 'Ten times cheaper': Russian space company testing iodine ...
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35 votes
3 answers
50k views

### How to programmatically calculate orbital elements using position/velocity vectors?

I would like to build some orbital mechanical software from scratch. I feel that this would be a great way to learn the steps required to calculate different Kepler orbital elements of an object, plot ...
• 5,926
48 votes
11 answers
40k views

### Could it be possible to launch a rocket from a balloon?

There are several (commercial) organisations looking into alternative means to launch space-bound rockets. One commonly proposed method is to use a large airplane as the launch platform. This method ...
• 583
25 votes
1 answer
4k views

### SpaceX's 4,425 satellite constellation - what's the method to the madness?

The BBC article SpaceX aims to launch internet from space discusses the SpaceX proposal for a dense array of over 4,000 LEO satellites for global internet coverage, and links to SpaceX non-...
• 148k
30 votes
4 answers
10k views

### How is the altitude of a satellite defined, given that the Earth is not spherical?

The altitude of a satellite is the distance between the Earth's surface and the satellite, but the Earth itself is not spherical. At the equator the Earth's radius is 21 km more than at the poles, and ...
10 votes
2 answers
4k views

### General guidelines for modeling a low thrust ion spiral?

I've been told that for low thrust ion spirals, delta V would be the difference between speeds of departure and destination orbits. For example the delta V between a 7.7 km/s LEO and a 3.1 km/s GEO ...
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26 votes
2 answers
2k views

### How did the tangential thrusters for the 2014 LDSD test spin-up then spin-down so nicely?

I just watched the NASA JPL video of the 2014 test of the Low-Density Supersonic Decelerator (LDSD). Tangential thrusters are used to spin up the craft for stability before the main rocket ignites. ...
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10 votes
2 answers
4k views

### How does one dogleg from Florida to a sun-synchronous orbit?

From NASA Spaceflight's article SpaceX Falcon 9 launches first NRO mission with NROL-76: The NROL-76 launch was not to be targeting a sun-synchronous orbit, typically used by the NRO’s optical ...
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35 votes
3 answers
38k views

### How much power would a spacecraft's magnetic shield require?

I've read over the decades that a magnetic shield might protect a spacecraft from cosmic radiation. Its a fascinating idea that might only be theory or science fiction at the moment. In regards to ...
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26 votes
4 answers
5k views

### Does the NK-33 engine require subcooled kerosene so cold that it turns to wax?

It was mentioned in this answer and in several other places on the internet that the kerosene fuel used by NK-33 engines needed to be subcooled enough so that it reached the same density as the LOX, ...
• 148k
48 votes
1 answer
37k views

### How often does ISS require re-boosting to higher orbit?

I know that ISS, being in low Earth orbit, requires regular boosts. But I can't seem to find information on how often does this happen. Is it done during each resupply mission, only during some of ...
• 695
59 votes
4 answers
56k views

### Why not build Saturn V's again?

Why is the US developing a new rocket and spacecraft as opposed to building the Saturn V and Apollo stacks again? The SLS / Orion development programs certainly can't cost less than the unit cost of ...
• 6,553
30 votes
1 answer
59k views

### What is the current cost-per-pound to send something into LEO?

As a student of economics and finance I would love to learn more about the cost structures of sending a payload into orbit. More specifically - What is the cost-per-pound to send something into LEO ...
• 5,926
7 votes
1 answer
750 views

### How can I verify my reconstructed gravity field of Ceres from spherical harmonics?

Based on @DavidHammen's very helpful answer I've made progress reconstructing the gravity field of Ceres from the Dawn radiometric data. The question there contains further information, but suffice it ...
• 148k
24 votes
5 answers
3k views

### How well can Voyager 1 separate Earth signals from Solar noise these days?

This is a follow-up question to Can Voyager 1 receive signals from Earth? this and this answer. UPDATED: see additional information and discussion below. As it continues to move farther from the Sun, ...
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10 votes
1 answer
5k views

### How have space suits dissipated the heat removed from astronauts?

I never thought about this until reading the comments below this answer. To radiate something like 150W (a very conservative lower limit of human + suit systems heat production - see @Uwe 's comment ...
• 148k
26 votes
10 answers
5k views

### Puzzler - which spacecraft(s) incorporated real wood structural elements?

Not a trick question, but a real puzzler - which spacecraft or spacecrafts incorporated real wood structural elements?
• 148k
8 votes
3 answers
1k views

### Why does Earth's atmospheric density have a big "knee" around 100 km? Is there a good analytical approximation?

I've used a quick very rough approximation of the drop of atmospheric density with altitude in this answer and in this answer by using a single exponential and scale height parameter, but that's not ...
• 148k
6 votes
2 answers
1k views

### Did the NASA PhoneSat actually try to use the GPS from the phone itself?

I was reading this article about NASA's PhoneSat Flight Demonstrations and came across this sentence. "To achieve this, NASA's PhoneSat design makes extensive use of commercial-off-the-shelf ...
• 148k
5 votes
1 answer
958 views

### Rotating in orbit?

Reading this question (Is the cupola, on the inside of the ISS, cold or warm to the touch?) prompted me to wonder about an object in orbit's orientation as it orbits its host object. For example, ...
• 2,668
4 votes
3 answers
873 views

### Has the Curiosity rover ever communicated directly with Earth via its high-gain antenna? Signal strength & data rate?

In the question How does Curiosity know how to point and move it's high gain antenna in real time? I show an image of the hexagonal, articulated high gain antenna on the curiosity rover, as well as ...
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208 votes
6 answers
22k views

### Can I borrow a lunar rover?

According to Wikipedia there are 3 LRVs sitting on the moon, in very well defined locations. Would China, or whomever gets to the moon with a person next, be able to get in and drive around in an LRV ...
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58 votes
7 answers
5k views

### How do we know the Apollo Moon landings are real?

Since about 1976, conspiracy theories denying the Moon landing and claiming it was all faked have cropped up. As a website devoted to answering questions about space exploration, we receive questions ...
53 votes
2 answers
46k views

### What is the purpose of the jets of water often under rocket engines during launch?

I have watched several STS launches, and noticed that there were always huge jets of water that would begin right before the rocket engines lit. They were right under the rocket, mounted to the pad. ...
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10 votes
2 answers
2k views

### How (the heck) are military satellites with (apparently) classified TLEs still showing up on sat map websites?

As I first noted in this comment I couldn't get TLEs for the recently launched OFEQ-11 spy satellites from space-track.com. When I looked at Search Resuls: OFEQ 11 Satellite details 2016-056A NORAD ...
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26 votes
3 answers
6k views

### How hard do you have to throw something off the ISS to make it deorbit?

During Expedition 41 Reid Wiseman and Alexander Gerst replaced a failed pump on the outside of the ISS. I am guessing they took the broken pump back inside the ISS and returned it to earth in one of ...
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19 votes
6 answers
8k views

### What artificial satellite has the farthest orbit around the Earth?

What is the furthest Earth orbiting satellite? What is its speed and purpose?
• 1
18 votes
3 answers
2k views

### What's the largest aperture telescope sent beyond the Earth-Moon system?

The question and answer about telescopes sent to different planets got me wondering. There are so many solar system bodies that have been photographed by deep space spacecraft, planets, dwarf planet(s?...
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15 votes
2 answers
6k views

### What is the ISS drag?

ISS constantly loses altitude to air drag and other forces (tidal, electromagnetic). While finding that rate in the sources isn't that hard, with orbital mechanics of altitude loss actually increasing ...
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9 votes
2 answers
1k views

### How do spacecraft measure their own charge?

The discussion in the NOAA legacy page Space Weather Prediction Center Topic Paper: Satellites and Space Weather (found here) lists: Types of Spacecraft Anomalies Spacecraft anomalies are ...
• 148k
5 votes
2 answers
1k views

### How can the two MarCO cubesats remain reliably close to InSight during their six month trip to Mars?

According to the NASA JPL web page Mars Cube One (MarCO) Mission Overview and the YouTube video MarCO: First Interplanetary CubeSat Mission linked there, after the Centaur upper stage deploys InSight, ...
• 148k
18 votes
3 answers
2k views

### How much can the Mars rover Curiosity do autonomously, after four years of operation?

I was under the impression (when asking this question) that over the past four years that experience by ground operators and programmers had lead to a configuration where the Mars rover Curiosity ...
• 148k
11 votes
5 answers
969 views

### Why doesn't thermal radio emission from a DSN "hot dish" completely swamp the benefits of a cold LNA?

The 70 meter DSN dishes are often used to receive the weakest signals, and so their receiver LNAs have cryogenic front-ends in an assembly that also contains a LHe refrigerator and vacuum system. If I ...
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