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11 votes
3 answers
3k 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 ...
uhoh's user avatar
  • 149k
17 votes
2 answers
11k 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 ...
Tommytii's user avatar
  • 173
18 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) ...
uhoh's user avatar
  • 149k
37 votes
4 answers
16k 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 ...
Tomislav Muic's user avatar
118 votes
6 answers
64k 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 ...
uhoh's user avatar
  • 149k
14 votes
3 answers
9k 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 ...
uhoh's user avatar
  • 149k
63 votes
8 answers
7k 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 ...
35 votes
7 answers
15k 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 ...
user's user avatar
  • 7,330
12 votes
3 answers
3k 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 ...
uhoh's user avatar
  • 149k
15 votes
1 answer
18k 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 ...
uhoh's user avatar
  • 149k
13 votes
1 answer
7k 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 ...
uhoh's user avatar
  • 149k
5 votes
2 answers
2k 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 ...
uhoh's user avatar
  • 149k
18 votes
1 answer
7k 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? ...
daniel.sedlacek's user avatar
14 votes
1 answer
2k 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 ...
SF.'s user avatar
  • 55k
4 votes
2 answers
466 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 ...
Phil Frost's user avatar
  • 1,033
17 votes
4 answers
4k 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 ...
uhoh's user avatar
  • 149k
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. ...
uhoh's user avatar
  • 149k
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 ...
uhoh's user avatar
  • 149k
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 ...
uhoh's user avatar
  • 149k
49 votes
11 answers
41k 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 ...
Nallath's user avatar
  • 593
39 votes
3 answers
59k 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 ...
Stu's user avatar
  • 5,928
30 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 ...
System Down's user avatar
  • 3,009
29 votes
4 answers
13k 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 ...
Sumit Agrawal's user avatar
27 votes
1 answer
5k 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-...
uhoh's user avatar
  • 149k
21 votes
2 answers
3k 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 ...
uhoh's user avatar
  • 149k
10 votes
2 answers
5k 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 ...
HopDavid's user avatar
  • 15.8k
60 votes
4 answers
61k 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 ...
dotancohen's user avatar
  • 6,784
26 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? and this and this answer. UPDATED: see additional information and discussion below. As it continues to move farther from the ...
uhoh's user avatar
  • 149k
10 votes
2 answers
5k 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 ...
uhoh's user avatar
  • 149k
1 vote
2 answers
960 views

What is the highest non-optical frequency used or tested for use in deep space communication?

For dish antennas used to transmit a signal over large distances, the on-axis gain scales as $D^2/ \lambda^2$ or $D^2 f^2 / c^2$ where $\lambda$ and $f$ are the wavelength or frequency and $c$ is the ...
uhoh's user avatar
  • 149k
212 votes
6 answers
24k 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 ...
James Jenkins's user avatar
27 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?
uhoh's user avatar
  • 149k
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, ...
uhoh's user avatar
  • 149k
21 votes
3 answers
25k views

How can I plot a satellite's orbit in 3D from a TLE using Python and Skyfield?

I have obtained a Two Line Element (TLE) of a satellite in Earth orbit from Celestrak at https://celestrak.org/NORAD/elements/ and I would like to use it to calculate an orbit. How can I calculate the ...
uhoh's user avatar
  • 149k
18 votes
1 answer
2k views

How strong and "hot" is the wind on the payload after the fairing is deployed at ~110km?

In the question What makes 21st century fairings so valuable that they'd potentially be recovered and re-used? I said: 21st century fairings are much more than passive rooftop boxes to "keep the ...
uhoh's user avatar
  • 149k
12 votes
2 answers
3k 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 ...
uhoh's user avatar
  • 149k
48 votes
1 answer
40k 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 ...
Viniter's user avatar
  • 695
30 votes
1 answer
60k 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 ...
Stu's user avatar
  • 5,928
28 votes
3 answers
7k 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 ...
user avatar
15 votes
2 answers
8k 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 ...
SF.'s user avatar
  • 55k
13 votes
5 answers
1k 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 ...
uhoh's user avatar
  • 149k
12 votes
2 answers
1k views

Why is FAI considering lowering the Karman Line to 80km?

I ran across this FAI statement The Karman line is the 100km altitude used by FAI and many other organisations to mark the “boundary” of space . In the last few years there have been many scientific ...
Machavity's user avatar
  • 7,905
11 votes
1 answer
6k 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 ...
uhoh's user avatar
  • 149k
10 votes
6 answers
1k views

Hijacked space data, notable instances of recovering images or other goodies from someone else's space mission?

These are images taken by a Chinese cubesat in lunar orbit, taken again by a Dutch radio telescope. The original of this GIF was tweeted here and I've reconstructed it because I don't know how to ...
uhoh's user avatar
  • 149k
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 ...
uhoh's user avatar
  • 149k
6 votes
1 answer
1k 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 ...
uhoh's user avatar
  • 149k
6 votes
2 answers
2k 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 ...
uhoh's user avatar
  • 149k
5 votes
1 answer
1k 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, ...
Milwrdfan's user avatar
  • 2,798
4 votes
3 answers
1k 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 ...
uhoh's user avatar
  • 149k
86 votes
7 answers
24k views

What can the KSP game actually teach about spaceflight and orbital mechanics, and what are its limitations?

I have seen at least several different users mention that they've found Kerbal Space Program helpful to understand issues of spaceflight and orbital mechanics. According to Wikipedia: While the game ...
uhoh's user avatar
  • 149k

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