72 votes

How did NASA prevent third parties from spoofing Apollo communications?

The signal from the Moon was received using giant parabolic antennas, e.g. the 64-m dish at the Parkes observatory. These have very good sidelobe rejection so they won't pick up any Earthbound signals....
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59 votes
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What would it take to get a message to another star?

The Arecibo raqdio telescope has a $300\ \mathrm m$ diameter mirror. Let's consider a radio wavelength of $3\ \mathrm{cm}$ ($10\ \mathrm{GHz}$) for convenience of arithmetic. That gives a diffraction ...
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49 votes

What is an "octet" in the context of NASA's LunaNET Interoperability Standard? ("internet on the Moon")

An octet is an 8-bit byte. Historically, "byte" wasn't always 8 bits (and still isn't, with some architectures having different byte sizes today); "octet" is unambiguous and widely ...
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46 votes
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First call to the moon 1969

Mission Control in Houston had a radio communication with the Apollo capsule as well as the Moon lander. A phone connection between the White House and Ground Control was established and connected to ...
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46 votes
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What was the last message to Opportunity today (13 Feb '19)?

From ArsTechnica: Late Tuesday night, scientists at NASA's Jet Propulsion Laboratory sent their final data uplink to the Opportunity rover on Mars. Over this connection, via the Deep Space Network, ...
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39 votes

Is Quantum Entanglement technology possible for interplanetary communication in future to achieve low real-time latency?

He replied that we actually received the signals in just 1-2 seconds with the help of MarCO CubeSats. Later on followed up with confusion from other users with his statement and asked for ...
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38 votes
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Why no recent information about or photos of Ultima Thule?

New Horizons was hidden behind the Sun a few days after the flyby, from January 4th to January 7th. Almost as soon as the encounter and earliest downlinks are over, New Horizons will go into solar ...
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35 votes
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What is an "octet" in the context of NASA's LunaNET Interoperability Standard? ("internet on the Moon")

Is "octet" just a fancy word for "byte" No, they mean very different things. A "byte" is the smallest unit of addressable memory of a specific CPU architecture. That ...
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34 votes

What would it take to get a message to another star?

@SteveLinton's answer is excellent and I'll just confirm below that its logic and numbers are correct. Then I'll show that you can do it optically as well, but with 10 meter telescopes instead of ...
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34 votes
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How do the Starlink satellites shine?

Starlink (and other satellites) categorically do not have exterior lights or illumination, that would be a waste of power for no particular benefit. The reason that we can sometimes see satellites ...
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31 votes

Apollo communication between the Earth and Moon

It can be seen through this Wikipedia article that all communication with the Apollo missions was done at about 2.2 GHz, which is well above the frequency that reflects on the Ionosphere (No higher ...
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30 votes
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Can I text on my cell phone from the ISS to Earth?

No. "200 km" is the shortest distance (actual ISS altitude varies but is closer to 400 than 200 km), but at that distance you're far outside the main lobe of the ground station antenna. Cellular ...
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30 votes

Why aren't space telescopes put in GEO?

Spacecraft are placed into the orbits that they need to be in, given the objectives of the mission and the constraints during design. Nothing in space is arbitrary, since there is so much at stake if ...
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29 votes
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Do astronauts go on a random banter with mission control like in the film 'Gravity'?

If you listen to live (or recorded) ISS to ground conversations you will find that the astronauts are human, and have perfectly normal conversations when not specifically running through mission ...
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28 votes
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Did USSR discontinue radio transmissions, relocate ships, to aid the US in response to Apollo 13?

According to NASA's Space Educator's Handbook: As the men in Apollo 13 experienced what no men had undergone before, millions followed the developing drama by radio and television in public squares, ...
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28 votes

Could we use a narrow paradigm, say laser, to get info faster from New Horizons? (With a moon base.)

It absolutely could happen, but it would require a more precise pointing than New Horizons has. Lasers of some kind are the best for the high data resolution. The spacecraft to most heavily use lasers ...
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27 votes
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If a Voyager crashes into something, would we know?

Most likely no. Voyager downlink communication (via its radio link to NASA's Deep Space Network (DSN) is not continuous. You can check the contact schedule at this Voyager site. If everything looks ...
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27 votes

Why no recent information about or photos of Ultima Thule?

In addition to the limited downlink time due to it being hidden behind the Sun, it should be noted that the New Horizons team is prioritizing downlinking the metadata of each of the images. This will ...
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  • 118k
26 votes

Where are the pictures during the time the pictures are sent from space to home?

Spacecraft that take pictures take them similar to a digital camera. However, the camera is very far away. Similar to downloading a movie off of a website so you can watch it on your local device, it ...
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26 votes
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Can Voyager 1 receive signals from Earth?

Yes, the Earth can send Voyager 1 a message as easily as we can receive a message. There are a few differences between the uplink and the downlink paths. We cannot upgrade the radio on Voyager 1 to ...
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26 votes
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Is Quantum Entanglement technology possible for interplanetary communication in future to achieve low real-time latency?

Apparently not: I like this Quora answer. Here's part of it, the rest is worth reading as well: No experiment conducted using entangled photons has ever demonstrated faster than light communication! ...
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26 votes
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What is carrier lock and bit lock?

First you lock on to energy at (or near) the expected frequency. That’s carrier lock. Then you start to look for patterns in how the phase changes. The transmitter is coding groups of bits as phase-...
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24 votes

How did NASA prevent third parties from spoofing Apollo communications?

The difference between 10 W at 350,000km, and 1,000 W at 1km is 131 dB. If the pranksters on Earth used a directional antenna like the Ham radio operators shown below, the ratio would be even higher ...
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24 votes

Why not send Voyager 3 and 4 following up the paths taken by Voyager 1 and 2 to re-transmit signals of later as they fly away from Earth?

It's a great question! Trajectory To get a few decades more out of them, you can launch Voyagers 3 and 4 sometime around now and get by with a maximally-boosting flyby of Jupiter since you wouldn't ...
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24 votes
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Why aren't space telescopes put in GEO?

It wouldn't need to turn as fast to stay focused, maybe increasing the lifetime of its reaction wheels. On Earth when you "turn" a telescope, you are really keeping it pointed in one direction! It's ...
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  • 148k
23 votes

Pictures from Mars

Let's compare with 4G, for which I could find some numbers: Your cell phone is transmitting with speeds of up to 50MBps with a maximum of 1 Watt (can be as low as a few µW!), using a tiny antenna ...
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  • 12.2k
22 votes
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Would adding satellites between Earth and Mars improve communications latency?

No. Communication latency (the time between sending a bit and receiving it on the other end) between Earth and Mars probes is limited almost entirely by the speed of light, as they are radio waves on ...
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  • 4,526
22 votes

Can we detect the cell phone, satellite phone, or walkie talkie of someone walking on Mars from Earth?

Maybe. Let's start with a known system that can communicate with Earth directly from Mars' surface: Curiosity's low gain antenna. This is driven by a 17 W transmitter and has 6 dB antenna gain (so ...
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22 votes

Will Curiosity and the Mars 2020 rover be able to communicate with each other via a Mars orbiter?

Yes, they could theoretically communicate with each other over the DSN, however in practice this will not happen (as it has no current uses). The amount of functions that Curiosity can perform ...
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