Astronomy and space exploration

Discussion in 'General Discussion' started by eloyc, Apr 10, 2017.

  1. KimB

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    You'd think. But private corporations are often much more cavalier about this sort of thing than government agencies. And government agencies aren't great at it. You'd think the corporations would be concerned about the reputations of their products, but I'm not sure that works out in practice.

    Because of how incredibly expensive it is to lift weight into orbit with rockets, it's highly unlikely that there are very wide engineering tolerances at play, regardless of the design. Building the rocket for more durability means adding weight, and adding weight means sacrificing payload. Rockets in general require much more fuel than payload. It looks like the StarHopper is intended to refuel in flight, but that too will be expensive.
     
  2. cheapchips

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    You're confusing up the Hopper with the actual Starship. The Hopper's not an orbital rocket. It won't fly higher than 500m. Possible source of confusion was the nosecone that fell over. That was pretty much made of tin foil but was only cosmetic. They decided not to make a second one. The tank section is made from quite hefty steel.

    The two Starship prototypes being built at the moment will be more as you describe. Their tanks are much thinner and are barely able to support their own weight. They won't be ready until later this year/early next so the Hopper lets them test a bunch of things in the interim.
     
  3. hoom

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    Ariane failure the other day

    2nd stage appears to have failed to ignite or outright separation fail.
    Comical commentator continuing to read the script for several mins despite obvious big problem & visuals switching to showing only troubled faces.
     
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  4. KimB

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    Ahh, okay. If it's just a tech test vehicle, then I'm not at all concerned.
     
  5. hoom

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    After a bit of a delay India has launched its first Moon lander.
     
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  6. eloyc

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    http://astronomy.com/news/2019/07/l...rst-spacecraft-to-change-orbit-using-sunlight
     
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  7. eloyc

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    https://www.space.com/nasa-tess-exoplanet-hunter-first-year.html
     
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  8. pharma

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    Tardigrades: 'Water bears' stuck on the moon after crash
    August 7, 2019

    [​IMG]

    [​IMG]


    https://www.bbc.com/news/newsbeat-49265125
     
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  9. cheapchips

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    I have mixed feelings in planetary preservation. It seems pretty important to the experts so who am I to argue. In the other hand, surely DNA sequencing for any carbon based life would identify it as being something you didn't bring with you.

    As for wiping out another planet's organisms, I say go for it. If a planet's life has been unable to make rockets after 4bn years they're too lazy for our respect. Plus we're really, really good at mass extinctions. :???:
     
    #509 cheapchips, Aug 7, 2019
    Last edited: Aug 7, 2019
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  10. eloyc

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    I have mixed feelings, as well. I assume that before sending humans to another planet we will already know if something's there. If we can't detect it by all reasonable means, maybe that means that life there doesn't play such an important role in the planet's biosphere. We don't even know if the mere fact of going there may destroy native organisms which we may have detected or not.

    At any rate, if there's life on another planet we can explore, I'm pretty sure we will find out so that the milestone of finding alien life may be achieved, no matter what
     
  11. tunafish

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    It's very unlikely to. The problem is not how it performs against normal rockets, it's how it performs against Hall effect thrusters.

    The reason VASIMIR was interesting when it was being designed was that the existing American ion drive tech was mostly gridded ion thrusters. Those were originally chosen because they were much easier to initially implement than the alternatives, but turned out to have a few hard to fix flaws that compromise their long-term reliability. Compared against them, VASIMIR seems like a very good solution, even though it's extremely complicated and complex and a lot of work needs to be done to make it practical.

    However, while the Americans were working with gridded thrusters, the Soviets poured all their ion drive research into Hall effect thrusters, and were much more successful than the Americans. Soviet/Russian HET are not experimental tech that needs a lot of new research; since the 70's, they have flown >240 thrusters in space with a 0% failure rate. In addition to reliable, HETs are structurally very simple, which also makes them light and cheap.

    NASA still spends some money on VASIMIR, but at this point it very much seems like HETs are the superior technology, and western satellite operators, which were very reluctant to use gridded-ion propulsion and not very interested in VASIMIR either seem to be willing to make the jump to HET.
     
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  12. eloyc

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    Today I was thinking about the transit method to detect planets. We already have TESS out there (just mentioning a recent example, not that this telescope is the first time we use this method), which is nice, but I wonder what are the chances that our tools are in the proper vantage point to study planetary systems... or that other planetary systems are aligned for us to be able to detect them this way.

    Also, I was thinking about direct imaging and how this method can improve over time. We already have pictures of protoplanetary discs, such as this one (HL Tauri):
    [​IMG]

    Which is of very high quality, IMO, so I wonder why is it so difficult to picture an exoplanet.

    Do you have any news on ongoing projects that aim to drastically improve the detection and even imaging of planets?
     
  13. nutball

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    It really depends on what you're trying to achieve. If you just want a picture, well then we already have those, but they are just dots. If you want a resolved image, or some even just some real science from the unresolved dot, then that's a different thing altogether.

    Of the most productive detection methods to date the transit method gives arguably the most information about the detected planets. Size and mass, giving at least some constraints on the composition, plus the potential to do atmospheric studies in the best cases. In terms of science bang for tax-payer buck this is currently the best value for money.

    Direct imaging is really, really difficult unless you choose your targets carefully. The primary reason it is so difficult is the contrast ratio between the host star and the reflected light from the planet. It works best in the cases that are almost diametrically opposed to the transit method, ie. large planets orbiting faint host stars (=> larger contrast ratios) at large orbital radii (=> larger angular separation on the sky). If you want an optical image of an Earth-like planet, and to maybe perform spectroscopy on the atmosphere to search for biomarkers, then these are not the planets you are looking for. These are the images we already have.

    After that life gets tough. You're talking very large mirror, probably space-based, maybe space-based interferometry. There are mission concepts, and have been for a long time now. Nothing particularly cheap though. I don't know what NASA might do, other than wait until after JWST is launched to commit that sort of money to another astronomy mission. The ESA roadmap at that mission scale is mapped out until the mid 2030s. As it stands everybody else is irrelevant. Some radical new concept might come along that does the whole thing on the cheap, or someone like Jeff Bezos decides to throw a few billion at the problem.
     
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  14. hoom

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    Yep JWST but also 30m Telescope & European Extremely Large Telescope are supposed to be capable, I think Giant Magellan is a marginal possibility
    [​IMG]
     
    #514 hoom, Aug 14, 2019
    Last edited: Aug 14, 2019
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  15. eloyc

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    I didn't know the OLT, and now I'm in love, so it hurts to read that "cancelled".

    Oh, regarding GMT, it won't be ready next year.
     
  16. nutball

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    Well, maybe. As I said it really depends what you mean by direct imaging of exoplanets. It's already been done from the ground, eg.

    https://en.wikipedia.org/wiki/HR_8799

    but note that the closest-in planet has an orbit at 14AU. That's between Saturn and Neptune in our own Solar System. Note also that they are gas giant planets a little larger than Jupiter.

    These new telescopes will be far better than Keck and allow imaging if planets in closer-in orbits. If you want images of a 1 Earth-radius planet in a 1AU orbit, well... we'll see. Earth is 9% of the radius of Jupiter, the projected surface area is less than 1% of Jupiter so the contrast ratio is >100 times smaller.

    Adaptive optics and nulling interferometry might get you there. TBH I'm a little out of the loop on the details of the instrumentation planned for these new larger telescopes. It has changed a lot over the years. You need to be a little careful about the way the capabilities are portrayed in the media, as a lot of the detail gets lost.
     
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  17. nutball

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    It's acronym was OWL.

    On astro-ph the other day was a concept for OWL-Moon. OWL, on the Moon:

    https://arxiv.org/abs/1908.02080
     
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  18. eloyc

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    So I'm in love with an OWL. Good to know. :mrgreen:

    I hope to live to see such a project become reality.
     
  19. hoom

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    Yeah that pic doesn't seem to have been kept up to date.

    I just love how it has so many mirrors in scale & how vastly bigger than anything before the 30m & ELT are going to be, super excited to see images from those & JWST.
     
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  20. rcf

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