20 votes
Accepted

What kind of signals and encodings were used to send tilt/pan commands to TV cameras on the Moon (up through Apollo)?

For the Ground-Commanded Television Assembly (GCTA) mounted on the rover that was used to image Apollo liftoffs from the moon: The real-time command messages consist of three vehicle address bits (...
7 votes

What is the maximum distance between two satellites orbiting at 400 km that would still allow them to communicate with each other using radio waves?

Imagine a circle (the circumference of the Earth) and a triangle with the angle points being the locations of the satellites and the centre of the Earth. (the centre of the circle) You can divide that ...
  • 7,551
6 votes

What antennas does JAXA use to communicate with its deep space spacecraft? Does it have a deep space network of its own?

Partial answer... Question: What antennas does JAXA use to communicate with its deep space spacecraft? From: https://www.isas.jaxa.jp/en/about/facilities/usuda.html (and mentioned in the comments to ...
6 votes

What is the maximum distance between two satellites orbiting at 400 km that would still allow them to communicate with each other using radio waves?

Probably not quite what you're looking for, but two satellites on opposite sides of Earth, 13542 km apart, can still stay in almost-uninterrupted contact via EME communications (bouncing the signal ...
6 votes

What is the maximum distance between two satellites orbiting at 400 km that would still allow them to communicate with each other using radio waves?

For line-of-sight communication it's not longer than $2\sqrt{ (6371+400)^2 - (6371)^2} = 4585$. Or $2\cos^{-1}\left(\frac{6371}{6371+400}\right)$ = 40 degrees, so 9 satellites at least.
  • 1,549
5 votes
Accepted

What is the maximum distance between two satellites orbiting at 400 km that would still allow them to communicate with each other using radio waves?

If, for example, you have only 2 satellites separated by half the distance (i.e., 21, 271 km), will they be able to communicate with each other? I guess not because Earth would be in the way. ...
4 votes
Accepted

Fjeldbo, Kliore, & Eshleman 1971 Fig. 22 planetary atmosphere index of refraction increasing with altitude; physics insight or convenient abstraction?

I thought I'd share some of my thoughts after reading the paper (I still need to read some sections in full detail), onto which hopefully someone actually knowledgeable in the field can comment. This ...
  • 1,476
4 votes
Accepted

How does the signal strength from the Voyager probe change with distance?

The signal strength decreases proportional to the inverse square of the distance. For double distance the strength is only 25 %. For 10 % more distance 17.36 % less signal.
  • 47.9k
3 votes
Accepted

Radio Telescope / DSN Node in L4 and/or L5

One significant issue is we cannot maintain a fixed baseline in this way. L4 and L5 are indeed stable, but in space (or rather, in the space that actually exists) "stable" does not mean ...
  • 7,990
3 votes

Would it be possible to receive the transmissions from JWST as an amateur?

Yes, it is possible to detect the S band telemetry from JWST as an amateur, and it has been done with a 6.1m dish. Hams have built dishes this big. The source you listed details this, and was written ...
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3 votes

What is this term in the link budget equation from Space Mission Analysis and Design (SMAD)?

Lpr and Lpt would be pointing loss, receiver and pointing loss, transmitter, respectively.
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3 votes
Accepted

Radio antenna used to communicate with the Telstar 1 satellite in 1962

I did not find a explicit comparison with a dish, but this quote does contrast the design with "other possible forms" The communications antenna at Andover is a much enlarged version of ...
3 votes
Accepted

How long did the plasma blackouts of Perseverance's signals to MRO and direct-to-Earth last during its seven minutes of terror?

There are some misunderstandings here (similar to this question) that make the question(s) a little malformed. Roughly what frequency was used in the link(s) between Perseverance and MRO? From ...
2 votes

Curiosity / MRO UHF connection and weak signal modulation

Another interesting paper is The Electra Proximity Link Payload for Mars Relay Telecommunications and Navigation (C.D. Edwards, et al., 2003), which is reference #21 in the DESCANSO paper @...
  • 6,352
2 votes

Curiosity / MRO UHF connection and weak signal modulation

The MSL DESCANSO article states that it is MRO that monitors the SNR and controls the data rate (section 2.2.2): In this mode of operations, it is the MRO radio that controls the return data rate, ...
2 votes
Accepted

Do we use masers, lasers or infrared lasers to send data from deep space back to Earth? If not, why not?

"Why don't current missions already use small masers..." So we have already been using conventional traveling wave tube amplifiers for microwave communications in space. Ka band is around 30 ...
  • 148k
1 vote

What is the maximum distance between two satellites orbiting at 400 km that would still allow them to communicate with each other using radio waves?

This depends on the wavelength. While short waves spread more like a light, long waves bend over horizon and can cover distances in excess of 17,000 km even from the surface of the Earth. This is more ...
  • 1,766
1 vote

What is this term in the link budget equation from Space Mission Analysis and Design (SMAD)?

As @TFC points out the $L_{p}$s are probably pointing losses due to pointing errors away from maximum gain. In this case the gains $G$ would have to be the maximum gains for ideally pointed antennas ...
  • 148k
1 vote

China, UAE and US all sending missions to Mars in 2020 (Summer of L̶o̶v̶e Mars); how far apart are their frequencies?

The Deep Space Network channel center frequencies are defined in the DSN Telecommunications Link Design Handbook, Document 810-005, Module 201, "Frequency and Channel Assignments". The ...
  • 6,352
1 vote

Why is the operating temperature for the Voyagers' receiver noise calculation about 1550K?

Having listened to CuriousMarc's excellent Apollo video and read the DESCANSO Chapter 3 document, there is no evidence that Voyager has any amplification prior to the mixer. At that time, at those ...
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1 vote

Why were the two Quindar tones so close in frequency and not apodized?

The Quindar system was used to reduce the risk of anybody with “Net 1” access inadvertently transmitting on the uplink. Net 1 talk was available at many worldwide places.

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