SpaceX Falcon 9 : TESS : April 18, 2018 : Discussion

[speedevil]

I am not sure if the transit time helps that much since the plane of the exoplanet's orbit may not be across the widest part of the star. I could be wrong, but I do not believe there is a way to tell if the transit is across a cord near the edge of the star, or across a diameter of the star.

There actually is.
Assuming the disk is a simple constantly illuminated circle (it's not).
If the 'impact' of the disk of the planet does not go all the way into the star, you get a curve that bumps up and smoothly down.
If it goes all the way in at any point, so you can see the whole disk of the planet silhuetted against the star, you get a constant brightness portion of the curve.
The ratio of brightness to the stars original brightness tells you the area of the planet, and you can look at the shape of the entry and exit to see how far 'up' the star is - as you go towards the limb of the star, the entries and exits are more gradual.

[jebbo]

Does anyone know if TESS is precise enough to measure the difference between "full transit" time (second contact to third contact) and "partial transit" time (first contact to fourth contact)? If it is, then it's possible to estimate the orbital period based on a single transit, assuming the mass and radius of the star are known. Even if that estimate is crude, it could be very helpful when observing subsequent transits if you want to know whether you missed any.

TESS 2 minute cadence certainly allows us to observe ingress & egress, but visibility depends on all sorts of other things (SNR, activity, etc), also this isn't essential anyway. Most planets have a low eccentricity, and transit duration depends on a/R*, so given R* you can get the period. For a lot of the TIC, R* is poorly constrained so you need follow up to get a more precise value.

I see I'm racing speedevil again , and as he says, you can tell whether you have a grazing transit or not.

--- Tony

[ChrisGebhardt]

Respectfully submitted: It's time to split this into separate UPDATES and DISCUSSION threads.

[ThePonjaX]

27 days? Doesn't this have to observe a star for 2 years to expect to catch at least one transit of an inner planet?

'No'.
It will detect a fraction of planets - naively for earthlike orbit planets about a twelfth, on one pass - though there are areas of the sky it will stare at for one year at a time (the poles).
It will detect all planets with orbits under 27 days multiple times.
In the zones of more continuous observation, it will detect all planets with periods up to about a year.

If the mission is approved and works for another two year survey of the same design, then you have about the same chance of detecting slower transiting planets you only caught once transiting again.
It would take about twenty years or more of observation to get to most planets with earth-like orbits with two transits so you can make a stab at their orbit.

However, there are many, many other instruments out there with synergies with TESS that may help complete the survey and followup on observations.

Observation pattern shown at:

Fantastic video.

About the steps to reach the final orbit: Is done on this way because the only way to do that? A limitation on technology avoid the possibility to get there directly? 

I've to say I'm really excited for this mission. 

[Greg Hullender]

TESS 2 minute cadence certainly allows us to observe ingress & egress . . .

Thanks. That's exactly what I was looking for.

For those interested in how one squeezes all sorts of useful information out of transit info, this paper, "Transits and Occultations," by Joshua N. Winn, is an excellent resource:

https://arxiv.org/pdf/1001.2010v5.pdf

[speedevil]

About the steps to reach the final orbit: Is done on this way because the only way to do that? A limitation on technology avoid the possibility to get there directly? 

It was designed for a very, very much smaller and less capable rocket than the F9.
A very early version of the F9 threw DSCOVR past the moon - TESS is even lighter. It could certainly do the entire job of the rockets first stage, and part of the second stage, and get it up to lunar encounter.

I think it is possible - I haven't run the numbers carefully - that starting from a near polar launch with a recovered F9, it can directly inject into the target orbit.
It would require about 4km/s, or so once in LEO.
The telescope would only mass perhaps 150kg, which helps somewhat with this.
(this also requires a very much longer coast than even the 'starman' one)

[Lar]

Probably too late to recalculate things now but why not change when the launcher was changed, if F9 can do a direct insertion, and TESS then has more stationkeeping capability, presumably?

[speedevil]

Probably too late to recalculate things now but why not change when the launcher was changed, if F9 can do a direct insertion, and TESS then has more stationkeeping capability, presumably?

I'm not sure it actually does any stationkeeping at all once in orbit.

The orbit it gets into is a resonant one with the moon, and according to the above video (around 7 minutes) is 'stable for decades'.

It may well be that there is nothing meaningful it could do with the extra fuel, if reaction wheel desaturations are not a driver of fuel use over the expected extended mission.

If the change in launcher was earlier, they would have been able to 'cheaply' gone from 4->9 cameras, and vastly improved scan speed/coverage.

[LouScheffer]

Probably too late to recalculate things now but why not change when the launcher was changed, if F9 can do a direct insertion, and TESS then has more stationkeeping capability, presumably?

I read where it already has enough fuel for a 20 year extended mission.   Most likely something else will fail first, or a better satellite will be launched so the analysis resources no longer make sense.

[Bubbinski]

I’m going to the TESS launch and will be at the Cape on April 16th. Already got the time off work, now arranging flights.

GO TESS!

[rockets4life97]

Did TESS slip to May? It wasn't mentioned as flying in April in the article for the Hispasat launch posted today.

[gongora]

Did TESS slip to May? It wasn't mentioned as flying in April in the article for the Hispasat launch posted today.

The article only mentioned flights through early April.  TESS is in mid April.

[Craig_VG]

Recent confirmation from Paul Hertz confirming still on schedule for April 16th:

https://twitter.com/jeff_foust/status/971050665647763456

[Tomness]

Posted a couple of days ago:

Moving @NASA_TESS into the clean tent @NASAKennedy where it will wait to meet the @SpaceX Falcon 9!

https://twitter.com/NASA_TESS/status/970737478926782467

Will TESS space craft be prepped, processed & encapsulated at Astrobotics facilities or SpaceX facilities?

[Jim]

Posted a couple of days ago:

Moving @NASA_TESS into the clean tent @NASAKennedy where it will wait to meet the @SpaceX Falcon 9!

https://twitter.com/NASA_TESS/status/970737478926782467

Will TESS space craft be prepped, processed & encapsulated at Astrobotics facilities or SpaceX facilities?

Neither.  It is already in the facility for those tasks.  PHSF.

[dsobin]

For those who are curious, PHFS is the NASA Payload Hazardous Servicing Facility.

[docmordrid]

For the more visually oriented,

https://science.ksc.nasa.gov/payload/lssm/facility/phsfbig.html

[NX-0]

That's some real 4th Grade stuff right there on a US Government webpage.
"Payload Hazardous Serviceing Facility (PHSF)"

For the more visually oriented,

https://science.ksc.nasa.gov/payload/lssm/facility/phsfbig.html

[mn]

That's some real 4th Grade stuff right there on a US Government webpage.
"Payload Hazardous Serviceing Facility (PHSF)"

For the more visually oriented,

https://science.ksc.nasa.gov/payload/lssm/facility/phsfbig.html

And some seriously misconfigured web server here too.
https://science.ksc.nasa.gov/payload/lssm/facility/images/
https://science.ksc.nasa.gov/images/

[speedevil]

https://science.ksc.nasa.gov/images/cdrom-1-95/img0014.jpg - for example - neat shuttle tile stuff.