Starship Asterisk*

JohnD wrote: ↑Sat Apr 21, 2018 9:04 am TESS is an exciting new probe, but lets face it, it's just another bit of space technology.

Isn't the continuing success of the Falcon9 the story? The twenty-fourth landing of the first stage! I've no idea just how much of that stage is reusable and will fly again, but this is a real space ship.
John

rstevenson wrote: ↑Tue Apr 24, 2018 3:29 pm
Interesting how close are the quantities of stars categorized as blue vs red, 1.3819 billion vs 1.3835 billion. Almost a tie.

orin stepanek wrote: ↑Tue Apr 24, 2018 11:31 am
Speaking of TESS; has it found anything yet?

• TESS is the new girl in town...how about something new from an old Gaia:

http://sci.esa.int/gaia/60176-call-for-media-second-data-release-from-esas-gaia-mission/ wrote:

---

Call for media: Second data release from ESA's Gaia mission, 19 April 2018

<<Media representatives are invited to a briefing on the second data release of ESA's Gaia mission, an astrometry mission to map more than one billion stars in our Galaxy, the Milky Way. The media briefing is being organised by ESA at the ILA Berlin Air and Space Show in Germany, on Wednesday 25 April 2018, 11:00–12:15 CEST. The show opens at 10:00 CEST.

Launched in December 2013, Gaia is destined to create the most accurate map yet of the Milky Way. By making high-precision measurements of the positions and motions of stars in the Milky Way, it will answer questions about the origin and evolution of our home galaxy.

The first data release in 2016, which contained positions of more than one billion stars plus distances and motions of a subset of two million, has already generated hundreds of scientific publications. The second data release is taking the census of our Galaxy to an entirely new level, including three-dimensional positions and two-dimensional motions of more than 1.3 billion stars, as well as their brightnesses and colours.>>

moontrail wrote: ↑Tue Apr 24, 2018 8:04 am

http://boards.4chan.org/sci/thread/9670 ... hread-tess

MarkBour wrote: ↑Mon Apr 23, 2018 4:31 pm
Now that I've looked at it a bit more, TESS will not be looking at a very large patch of sky in a given month, and is always facing its cameras almost straight away from the Sun when in science mode. Eclipses that would cause it to lose power sound like they would be a bad thing. I also find it interesting that TESS has to exit science mode and reorient to download data. I wonder why it could not have been designed in a way that did not require that.

Chris Peterson wrote: ↑Sat Apr 21, 2018 1:08 pm Boring. A rocket is just a bus.

alter-ego wrote: ↑Sun Apr 22, 2018 6:17 am

MarkBour wrote: ↑Sun Apr 22, 2018 4:48 am

alter-ego wrote: A very interesting and non-intuitive orbit:

That's pretty nice. When they say it required no eclipse to exceed 6 hours, do they mean no eclipse of any of the stars in the survey? So, for example, this orbit never has any of its view blocked by either the Earth or the Moon for more than 6 hours at a time? Probably no point on the sky at all, since I understand that the stars it will be observing will be all over the sky ...

Good question. The paper is not clear except it only refers an eclipse condition when TESS is in the Earth's shadow (from the Sun). This article mentions long eclipses as a concern for power drain/loss when the solar arrays are aren't illuminated. Since heaters are used to keep the core electronics operational, extended cold-soaks during eclipses increases the power drain further. The bottom line is it's critical to avoid a mission failure due to power loss, and there's not much margin in battery life therefore TESS needs the Sun virtually all the time.

MarkBour wrote: ↑Sun Apr 22, 2018 4:48 am

alter-ego wrote: A very interesting and non-intuitive orbit:

A High Earth, Lunar Resonant Orbit for Lower Cost Space Science Missions (2013) wrote: The orbit-parameter selection process for the P/2-HEO was driven by three constraints imposed by TESS:
1) no eclipse can exceed 6 hours duration during the 4-year mission; 2) maintain mission-orbit perigee above
GEO (>6.6 RE) for four years; and 3) maintain mission-orbit perigee below 22 RE for four years to ensure
robust communications.
...

That's pretty nice. When they say it required no eclipse to exceed 6 hours, do they mean no eclipse of any of the stars in the survey? So, for example, this orbit never has any of its view blocked by either the Earth or the Moon for more than 6 hours at a time? Probably no point on the sky at all, since I understand that the stars it will be observing will be all over the sky ...

alter-ego wrote: A very interesting and non-intuitive orbit:

A High Earth, Lunar Resonant Orbit for Lower Cost Space Science Missions (2013) wrote: The orbit-parameter selection process for the P/2-HEO was driven by three constraints imposed by TESS:
1) no eclipse can exceed 6 hours duration during the 4-year mission; 2) maintain mission-orbit perigee above
GEO (>6.6 RE) for four years; and 3) maintain mission-orbit perigee below 22 RE for four years to ensure
robust communications.
...

APOD Robot wrote: ↑Sat Apr 21, 2018 4:05 am ...
In the coming weeks, TESS will use a series of thruster burns to boost it into a high-Earth, highly elliptical orbit. A lunar gravity assist maneuver will allow it to reach a previously untried stable orbit with half the orbital period of the Moon and a maximum distance from Earth of about 373,000 kilometers (232,000 miles). From there, TESS will carry out a two year survey to search for planets around the brightest and closest stars in the sky.

• Periodic perigee range from 8.4 earth radii (R_e) to 20.9 R_e
• Periodic ecliptic inclination from 21°to near 50°(21°< Inclination < 40°over mission lifetime)
• No station keeping over the mission duration (currently scheduled for 2 years)

A High Earth, Lunar Resonant Orbit for Lower Cost Space Science Missions (2013) wrote: The mission orbit selected for TESS early in the design process was the “P/2-HEO,” a high Earth orbit in
2:1 resonance with the Moon (i.e., having an orbital period of 13.7 days), first studied in depth by McGiffin [2]
and similar to the 3:1 lunar-resonant orbit of the IBEX mission [3]. The P/2-HEO is eccentric, with perigee
above geostationary altitude (GEO) and apogee beyond the Moon’s orbital radius. The spacecraft reaches this
orbit via a gravity-assist flyby of the Moon. The P/2-HEO was selected for TESS to provide unobstructed
observation sectors and continuous light curves for the TESS all-sky survey. Although TESS was the model
for this study, the results contained herein apply to space missions of any size that require a similar operating
environment and seek a low-V option.
...
The orbit-parameter selection process for the P/2-HEO was driven by three constraints imposed by TESS:
1) no eclipse can exceed 6 hours duration during the 4-year mission; 2) maintain mission-orbit perigee above
GEO (>6.6 RE) for four years; and 3) maintain mission-orbit perigee below 22 RE for four years to ensure
robust communications.
...
The P/2-HEO analysis draws upon on the initial work of McGiffin [2]. A key result of this work is that
“lunar secular perturbations average, roughly, to zero, resulting in significant long term stability” when the
spacecraft apogee is offset 90 deg with respect to the Moon and when spacecraft apogees alternately lead
and trail the Moon, as shown in the Earth-Moon rotating coordinate system in Fig. 1(a). Figure 1 shows the
3.5 phasing orbits, the transfer orbit, and the 25-year propagation of the P/2-HEO mission orbit, including
plots of the orbital elements. Although the orbit is high and subject to lunisolar perturbations, a proper
selection of initial conditions—in conjunction with resonance with the Moon—drives the orbital elements of
the P/2-HEO to oscillate rather than grow or shrink without bound. Much of the subsequent analysis focuses
on finding those initial conditions that ensure such non-secular behavior and ensure that the oscillations are
bounded by the mission’s eclipse and perigee-range constraints.

heehaw wrote: ↑Sat Apr 21, 2018 11:07 pm
I remember my young brother decades ago at his first job being amazed at people measuring things to a thousandth of an inch.

heehaw wrote: ↑Sat Apr 21, 2018 11:07 pm
Well LIGO measures things to a tiny fraction of the diameter of a single proton. And the signal came through, loud and clear!

https://www.sciencenews.org/article/how-ravens-caused-ligo-data-glitch?utm_source=editorspicks042218&utm_medium=email&utm_campaign=Editors_Picks wrote:
How ravens caused a LIGO data glitch
By Emily Conover, Science News, April 18, 2018

<<While the data was amassing, suddenly there came a tapping, As of something gently rapping, rapping at LIGO’s door.

A microphone sensor that monitors LIGO’s surroundings caught the sounds of pecking birds on tape in July 2017, Berger, of the LIGO Laboratory at Caltech, said. So the crew went out to the end of one of the detector’s 4-kilometer-long arms to check for evidence of the ebony birds at the scene. Sure enough, frost covering a pipe connected to the cooling system was covered in telltale peck marks from the thirsty birds. One raven, presumably seeking relief from the desert heat, was caught in the act. Altering the setup to prevent ice buildup now keeps the ravens from tapping, evermore.>>

scr33d wrote: ↑Sat Apr 21, 2018 9:47 pm

Chris Peterson wrote: ↑Sat Apr 21, 2018 4:35 pm

JohnD wrote: ↑Sat Apr 21, 2018 4:24 pm The real technology that people should be in awe of are the science and engineering behind TESS, LIGO, the upcoming LISA, etc., but it is much harder for people to appreciate those because of the physics.

LIGO is simply fantastic! I remember my young brother decades ago at his first job being amazed at people measuring things to a thousandth of an inch. Well LIGO measures things to a tiny fraction of the diameter of a single proton. And the signal came through, loud and clear! Hallelujah!

Chris Peterson wrote: ↑Sat Apr 21, 2018 4:35 pm

JohnD wrote: ↑Sat Apr 21, 2018 4:24 pm Well, I was being provocative, and Chris either fell for bit, or (more likely) called my bluff!

But I do still feel that an even half reusable launch rocket is a step towards a truly space faring culture. After all, if we could find evidence of life elsewhere, unless future technologies can transport us there from the surface of Earth ( as likely as FTL, I imagine) we'll go one being BillyNoMates if we have to launch a brand new ship every time.

What I'm not convinced of is that having this type of rocket with a reusable component is necessarily economically important. If we ultimately colonize the Solar System (I disregard anything beyond that as pure fantasy), perhaps in a Kim Stanley Robinson sort of future, I don't think we're going to be using that sort of rocket at all (a brute force bucket of fuel and a rocket engine), but rather, something more akin to an airplane. Rockets of the sort we currently have stand to hugely increase our pollution problems if they get used much more than now.

Chris Peterson wrote: ↑Sat Apr 21, 2018 1:08 pm

JohnD wrote: ↑Sat Apr 21, 2018 9:04 am impressive about the Falcon, just a modification of dozens of other designs. Not even clear that landing the first stages will be cost effective in the long run. No, what's interesting is the "space technology".

What would be REALLY interesting would be the Space Elevator: https://en.wikipedia.org/wiki/Space_elevator
we could ALL go to the moon if we were so foolish as to wish to do so. (Mars is worse.)

JohnD wrote: ↑Sat Apr 21, 2018 4:24 pm Well, I was being provocative, and Chris either fell for bit, or (more likely) called my bluff!

But I do still feel that an even half reusable launch rocket is a step towards a truly space faring culture. After all, if we could find evidence of life elsewhere, unless future technologies can transport us there from the surface of Earth ( as likely as FTL, I imagine) we'll go one being BillyNoMates if we have to launch a brand new ship every time.

dbooksta wrote: ↑Sat Apr 21, 2018 2:16 pm It looks like there's so much going on in that photo. Can anyone provide annotated commentary on the features of that section of the rocket?

Chris Peterson wrote: ↑Sat Apr 21, 2018 1:08 pm
Boring. A rocket is just a bus. A bit of an improvement over ancient Chinese fireworks, but that's all. Nothing very impressive about the Falcon, just a modification of dozens of other designs. Not even clear that landing the first stages will be cost effective in the long run.

Chris Peterson wrote: ↑Sat Apr 21, 2018 2:36 pm

richard schumacher wrote: ↑Sat Apr 21, 2018 2:21 pm
That attitude is surprising. By making the boring old bus an order of magnitude less expensive and more reliable we can launch more scientific instruments. This is a good thing. You would hesitate sending your kids to school if each trip cost $20 and had a few percent chance of killing them.

Oh, I didn't say it isn't useful. But it's just engineering, not science. We live in a golden age of engineering, where we can make almost anything that we can imagine. In this story, it is TESS that is exciting, not the bus that gets it to its destination.

richard schumacher wrote: ↑Sat Apr 21, 2018 2:21 pm

Chris Peterson wrote: ↑Sat Apr 21, 2018 1:08 pm Boring. A rocket is just a bus. A bit of an improvement over ancient Chinese fireworks, but that's all. Nothing very impressive about the Falcon, just a modification of dozens of other designs. Not even clear that landing the first stages will be cost effective in the long run.

That attitude is surprising. By making the boring old bus an order of magnitude less expensive and more reliable we can launch more scientific instruments. This is a good thing. You would hesitate sending your kids to school if each trip cost $20 and had a few percent chance of killing them.

Chris Peterson wrote: ↑Sat Apr 21, 2018 1:08 pm Boring. A rocket is just a bus. A bit of an improvement over ancient Chinese fireworks, but that's all. Nothing very impressive about the Falcon, just a modification of dozens of other designs. Not even clear that landing the first stages will be cost effective in the long run.

JohnD wrote: ↑Sat Apr 21, 2018 9:04 am TESS is an exciting new probe, but lets face it, it's just another bit of space technology.

Isn't the continuing success of the Falcon9 the story? The twenty-fourth landing of the first stage! I've no idea just how much of that stage is reusable and will fly again, but this is a real space ship.
John