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70 votes

Have we attempted to experimentally confirm gravitational time dilation?

You don't need a space probe. Or an aircraft. Or even a car. NIST has measured the predicted general relativity time dilation due to a change in altitude on Earth of one foot!
Mark Adler's user avatar
  • 58.2k
52 votes

Have we attempted to experimentally confirm gravitational time dilation?

In addition to specific probes like the one mentioned by called2voyage, the effect is significant enough that it affects everyday operations. For example, the GPS constellation needs regular clock ...
Bear's user avatar
  • 1,565
42 votes
Accepted

What does NASA mean when they use the term 'PDT (ERT)'

ERT is Earth Received Time. I.e., when we find out about the event. source
Organic Marble's user avatar
40 votes

Have we attempted to experimentally confirm gravitational time dilation?

Yes, time dilation was experimentally confirmed by Gravity Probe A, launched by NASA on June 18, 1976. The clock rates of two masers (one on the probe and one on Earth) were compared, and it was ...
called2voyage's user avatar
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26 votes
Accepted

Why would astronauts need a wristwatch and a separate timer?

(Shuttle-centric answer, but concept likely applies to other spacecraft, especially involving crew who flew on the shuttle) "Egg timers" were utilized heavily on the shuttle to time multiple ...
Organic Marble's user avatar
23 votes
Accepted

New Year's Celebration on the ISS

The official time zone is GMT, or UTC. As for the number of times they could celebrate, well, that's a bit tricky. The station goes towards the east, which is actually backward in time. There are a ...
PearsonArtPhoto's user avatar
  • 121k
21 votes
Accepted

How can we transmit a date to another species?

The approach taken by Voyager Golden Record is through use of pulsars. Unlike the insane exponents needed to utilize microscopic physical phenomena or planck time, pulsars operate on ~1 second ...
SF.'s user avatar
  • 55k
21 votes

How do launches avoid leap seconds? Why?

It's not just launches. It's, well, everything. It drives me nuts! Spacecraft flight software almost always have the capability to execute uplinked commands based on time. But what time scale? The ...
David Hammen's user avatar
21 votes

What is the time dilation between Mars and Earth resulting from the mass difference?

From my answer to Parker Solar Probe passing extremely close to the Sun; what relativistic effects will it experience and how large will they be?: From here (or here if you are ambitious) the lowest ...
uhoh's user avatar
  • 149k
19 votes
Accepted

Are there multiple types of UTC time?

I think there's two important ways to think of them: these are the UTC implementations; when you need to know the time now, precisely, these are the current time references you can use. Actual UTC ...
Erin Anne's user avatar
  • 12k
18 votes
Accepted

How do launches avoid leap seconds? Why?

Avoiding leap seconds is easy, don't launch at June 30th or December 31st when a leap second is announced, see https://en.wikipedia.org/wiki/Leap_second It is difficult to test if leap seconds during ...
Uwe's user avatar
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17 votes
Accepted

Is GPS time at least "really close" to TAI (International Atomic Time)?

TL;DR: For all practical purposes except milliarcsecond radio astronomy, TAI and GPS time are separated by exactly 19 seconds. TAI and GPS time both attempt to represent time as ticked by an ideal ...
David Hammen's user avatar
17 votes

How does time work on other planets?

Some basics: Every planet, moon or asteroid have their own rotation period along some specific axis. In very good approximation the period is constant (but not exactly). So every celestial body has ...
Heopps's user avatar
  • 9,061
16 votes

How much light is there on the way from Earth to Proxima Centauri?

No, the power collected by solar panels is reduced by the square of the distance from the light source. At the Earth's distance from the sun, the energy of sunlight is about 1300 watts per square ...
Russell Borogove's user avatar
16 votes

New Year's Celebration on the ISS

I was interested in the bonus question and decided to do an ad-hoc survey using ISS Tracker in historical mode. I entered the appropriate 2020-01-01 00:00:00 for each apparently relevant time zone (-...
Seth Robertson's user avatar
16 votes

Why would astronauts need a wristwatch and a separate timer?

As mentioned in another answer to your question, astronauts may need to time multiple events. Also using multiple clocks helps to detect if one clock is wrong. In fact Buzz Aldrin famously wears three ...
Steve Pemberton's user avatar
13 votes
Accepted

How far from earth have atomic clocks (or ultra-stable oscillators) been placed and monitored?

There was Rb-based Ultra Stable Oscillator in outer space, delivered to Titan (VI moon of Saturn) inside the Huygens, brought there by Cassini. (DWE RUSO in http://nssdc.gsfc.nasa.gov/image/spacecraft/...
osgx's user avatar
  • 2,315
13 votes
Accepted

Which Earth time zone most closely matches the ISS astronauts' daily schedule?

The wake/sleep cycle actually does use GMT. It was chosen as a compromise between Moscow time and Houston time. That permits times for meetings between the ISS crew and personnel in either city during ...
Mark Adler's user avatar
  • 58.2k
12 votes
Accepted

What kind of time regiment/schedule do ISS astronauts have?

Like a lot of things that should be readily available, it's frustratingly difficult to find this on any NASA web site. Fortunately ESA came to the rescue in the form of a blog post about Alexander ...
Organic Marble's user avatar
12 votes

Apollo Missions - Travel time to moon

Escape velocity is the velocity at a given altitude (usually the surface) that is enough to leave the body's sphere of influence with a positive net velocity. But if you leave a body at exactly escape ...
Nathan Tuggy's user avatar
  • 4,567
10 votes

How does GPS receiver synchronize time with GPS satellites?

The problem The GPS receiver's time has to be synchronized with atomic clocks located in GPS satellites. It is kinda chicken or the egg problem. The receiver needs precise time to calculate precise ...
Vlastimil Ovčáčík's user avatar
10 votes

How long would it take to travel to Proxima b?

5.8 years According to this page, distance travelled under constant force acceleration, even up to relativistic speeds, is calculated by: $s(t) = c(\frac{m_0c}{F})(\sqrt{1 + (\frac{F}{m_0c})^2t^2} - ...
MichaelK's user avatar
  • 1,819
9 votes

Juno to Jupiter Budget

Was that option considered in detail? Almost certainly not. This question is based on the false assumption that staffing levels remain more or less constant across all phases of flight. This is not ...
David Hammen's user avatar
9 votes

Which Earth time zone most closely matches the ISS astronauts' daily schedule?

I called a retired NASA employee to check on this question. And the answer is GMT+0. I also found this answer: https://www.astronautabby.com/the-international-space-station-time/ Here is the answer ...
Greg Hogue's user avatar
8 votes

How can we transmit a date to another species?

Our basic unit of time, the second, is officially defined in terms of physical phenomena, so our messages have to get that across. If the aliens and ourselves have a compatible understanding of ...
Russell Borogove's user avatar
8 votes

How long will it take for Starman to get to Mars?

Don't know how specific you want, but at 7:59 AM - 6 Feb 2018 Elon tweeted About 2.5 hours to T-0 for Falcon Heavy. Watch sim for highlight reel of what we hope happens. Car actually takes 6 months ...
BruceWayne's user avatar
  • 1,063
8 votes
Accepted

How are Spacecraft Event Times (SETs) managed; to what timescales are they linked?

From my experience: Ground operators work with UTC. All events are time tagged with UTC time stamps. This is a bit of a hassle for programmers who have to deal with leap seconds, but makes everything ...
Mefitico's user avatar
  • 1,987
8 votes
Accepted

What specific event determined the "end" of a shuttle mission?

Flight Durations are determined from the time of liftoff to MLG Touchdown, specified in days, hours, minutes, and seconds. MLG = Main Landing Gear Space Shuttle Missions Summary page 1-2 STS-1 ...
Organic Marble's user avatar
8 votes

How does time work on other planets?

Currently, UTC is the basis for time that is used across the Solar System (edit: not in science, however). You not only could, but would have to have a universal time in a future universe. It's a good ...
Therac's user avatar
  • 208
8 votes

Has anyone seriously considered a space-based time capsule?

future Perhaps a time capsule will feature prominently in one of these: What would be the (most difficult) challenge to make a 10,000 year satellite? microfilm Answers to Is there really microfilm on ...
uhoh's user avatar
  • 149k

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