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What Time Is It on the International Space Station? (2013)

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Re: What Time Is It on the International Space Station? (2013)

#21

Post by clamprecht »

I think they actually have a separate time called OBT (maybe it stands for Orbit).

I was at the Johnson Space Center in Houston recently, where we got a tour of the live Mission Control room for the International Space Station. I noticed two clocks at the top of one of the screens. One was GMT, the other was "OBT", and the OBT clock was around 17 seconds ahead of GMT. I think it has to do with relativity, and the fact that the space station is moving relatively faster than the earth. Maybe someone can confirm.

I got a photo of this mission control monitor if anyone is interested.

Re: What Time Is It on the International Space Station? (2013)

#22

Post by philliphaydon »

rocqua wrote: post #14
dfox wrote: post #4

I find it somewhat interesting that when SpaceX's streams switch to views with burned-in timecode it is always in UTC. Edit: and usually in ISO8601-ish format

If you are going to design something using a time code the most obvious solution is probably to choose your own zone. When you realize that doesn't apply to anyone else, UTC is the next option. Especially because it means you don't need to deal with user configuration. As for ISO8601, that probably results from people looking for some standard to help with compatibility. If you just mean YYYY-DD-MM HH:MM that is just…

It’s yyyy-mm-dd not yyyy-dd-mm....

Re: What Time Is It on the International Space Station? (2013)

#23

Post by jharohit »

clamprecht wrote: post #21

I think they actually have a separate time called OBT (maybe it stands for Orbit). I was at the Johnson Space Center in Houston recently, where we got a tour of the live Mission Control room for the International Space Station. I noticed two clocks at the top of one of the screens. One was GMT, the other was "OBT", and the OBT clock was around 17 seconds ahead of GMT. I think it has to do with relativity, and the fac…

If you know the clock drift, won't you be able to calibrate the space station clock back to GMT+0, thus eliminating the need for an OBT?

Re: What Time Is It on the International Space Station? (2013)

#24

Post by Pxtl »

admp wrote: post #3
aynsof wrote: post #2

It's weird that the author chooses Iceland as an example of a GMT+0 country, rather than Britain which is where Greenwich is.

Unlike Britain, Iceland does not have Daylight Saving Time, and therefore is GMT+0 throughout the year.

Am I the only programmer who is suddenly super duper envious of Iceland?

Re: What Time Is It on the International Space Station? (2013)

#25

Post by dannyw »

jharohit wrote: post #23
clamprecht wrote: post #21

I think they actually have a separate time called OBT (maybe it stands for Orbit). I was at the Johnson Space Center in Houston recently, where we got a tour of the live Mission Control room for the International Space Station. I noticed two clocks at the top of one of the screens. One was GMT, the other was "OBT", and the OBT clock was around 17 seconds ahead of GMT. I think it has to do with relativity, and the fac…

If you know the clock drift, won't you be able to calibrate the space station clock back to GMT+0, thus eliminating the need for an OBT?

GMT is already corrected back to earth GMT. But if you’re doing a time sensitive measurement and went to measure real seconds, you look at OBT.

Re: What Time Is It on the International Space Station? (2013)

#26

Post by userbinator »

clamprecht wrote: post #21

I think they actually have a separate time called OBT (maybe it stands for Orbit). I was at the Johnson Space Center in Houston recently, where we got a tour of the live Mission Control room for the International Space Station. I noticed two clocks at the top of one of the screens. One was GMT, the other was "OBT", and the OBT clock was around 17 seconds ahead of GMT. I think it has to do with relativity, and the fac…

+17s would not be due to time dilation, neither in magnitude nor sign; references I could find show that time on the ISS is slower than on Earth by around 14ms per year, and the ISS has been on orbit for less than 20 years.

Re: What Time Is It on the International Space Station? (2013)

#29

Post by icegreentea2 »

clamprecht wrote: post #21

I think they actually have a separate time called OBT (maybe it stands for Orbit). I was at the Johnson Space Center in Houston recently, where we got a tour of the live Mission Control room for the International Space Station. I noticed two clocks at the top of one of the screens. One was GMT, the other was "OBT", and the OBT clock was around 17 seconds ahead of GMT. I think it has to do with relativity, and the fac…

OBT (I'm guessing onboard time actually), is probably using GPS time (https://en.wikipedia.org/wiki/Global_Positioning_System#Time...) which is now 18 seconds ahead of UTC due to additional leap seconds inserted into UTC since GPS time started.

Re: What Time Is It on the International Space Station? (2013)

#30

Post by jcranmer »

jackfoxy wrote: post #7
juststeve wrote: post #5

Earlier quoted context omitted.

i read somewhere that some people may not like referring to britain as the default 'reference point' for timezones due to political/cultural reasons of their country. personally i dont have an issue with it, and i'm not saying that's the case here, maybe the author just likes iceland?

The UK developed the first portable timepiece good enough to accurately tell longitude. It's theirs.

To be slightly more accurate: in the 1880s, the British Empire had the preeminent navy and thus the preeminent naval charts. While other countries (including the US) maintained more local meridians for doing geodetic surveys of their own countries, it was the Greenwich Meridian that tended to dominate naval charts, which meant that it was more or less a de facto standard anyways by the Meridian Conference.
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