<p>If the starshade was to stay in place over the ground telescope, it would have to be in a geosynchronous orbit, which puts it almost 36,000 km from Earth's surface. To cover an angular distance of 1 arcsecond (1/3600 of a degree), it would have a size of around 10km. Certainly not impossible, but technologically impractical at the moment. Also, the starshade would only shade a small region of the sky, so it wouldn't be useful from other observing sites.</p>

<p>As for the space telescopes using a starshade in geosynchronous orbit; that would be impossible, at least for scopes orbiting Earth, like Hubble is. The starshade is orbiting Earth at a different distance, and therefore speed, than the telescopes. As far as I can see, it would be near impossible to keep them aligned for anything more than a few minutes. I haven't done any number-crunching on this, though.</p>

CC BY-SA 3.0
2017-08-13T17:25:31.543Z
Maybe one can find two synchronized halo orbits at the Moon? A telescope in GEO is of course another solution, which allows for smaller star shade.
LocalFluff
CC BY-SA 4.0
2024-06-20T00:05:05.127Z
Winning answer! Except the starshade wouldn't have to cover an arcsecond. That would block the star's planets too, as well as the nearby stars. You'd only block the star itself which is ~ a milliarcsecond. So the occultor would only need to be 10 meters wide.
Miss Understands
CC BY-SA 3.0
2017-08-10T22:22:44.767Z
2017-08-10T22:22:44.767Z
Jim421616
<p>1) Could a <a href="http://www.jpl.nasa.gov/news/news.php?release=2014-089" rel="noreferrer">starshade</a> in orbit be used by ground based telescopes? If so, what kind of orbit should it have?</p>

<p>2) Could the same starshade be used by two different space telescopes, or does the positioning make it impractical?</p>

CC BY-SA 3.0
2015-04-02T15:36:03.910Z
To what end would 1) be intended? If the purpose is to block all unwanted light, putting an atmosphere between the telescope and the shade when your signal is the light from an exoplanet, would the noise not overpower signal by several magnitudes? 2) sounds impossible given the proposed depth of the shade, but even if it were 2D, at some point in order to maintain alignment with the planet one of the telescopes would have to move between the shade and the second telescope.
Mitch Goshorn
CC BY-SA 3.0
2015-04-02T15:52:46.780Z
@MitchGoshorn Fantastically enough, they can already make [direct imaging of exoplanets](http://www.wired.com/2008/11/first-direct-im/) from the ground using coronagraphy inside the telescope.
LocalFluff
CC BY-SA 3.0
2015-04-02T16:00:06.357Z
I guess this signal to noise problem isn't an issue afterall, though as the linked article says, the observed planets are putting out more light than an 'Earth-like' planet would. But frankly coronagraphy seems like a lot more practical as the telescopes own tracking would maintain alignment.
Mitch Goshorn
CC BY-SA 3.0
2015-09-20T08:14:01.310Z
I was going to ask the same question, but with a high-altitude drone (or such) instead of a satellite. The satellite would need to avoid apparent motion relative to the stars, which would be difficult to impossible. The nearest I can imagine is a highly elliptical orbit with the apoapsis velocity equal to the ground velocity at the observatory. You'd need an array of such shade-satellites, and you'd have to move them all when switching to a new target.
Blackbody Blacklight
<telescope><space-telescope>
Can ground based telescopes use a starshade in space?
LocalFluff
# Can ground based telescopes use a starshade in space?

(Asked by: username_0 on 2015-04-02)

1) Could a [starshade](http://www.jpl.nasa.gov/news/news.php?release=2014-089) in orbit be used by ground based telescopes? If so, what kind of orbit should it have?

2) Could the same starshade be used by two different space telescopes, or does the positioning make it impractical?

**Tags:** telescope, space-telescope

> **Comments:**
> **username_1**: To what end would 1) be intended? If the purpose is to block all unwanted light, putting an atmosphere between the telescope and the shade when your signal is the light from an exoplanet, would the noise not overpower signal by several magnitudes? 2) sounds impossible given the proposed depth of the shade, but even if it were 2D, at some point in order to maintain alignment with the planet one of the telescopes would have to move between the shade and the second telescope.  
> **username_0**: @username_1 Fantastically enough, they can already make [direct imaging of exoplanets](http://www.wired.com/2008/11/first-direct-im/) from the ground using coronagraphy inside the telescope.  
> **username_1**: I guess this signal to noise problem isn't an issue afterall, though as the linked article says, the observed planets are putting out more light than an 'Earth-like' planet would. But frankly coronagraphy seems like a lot more practical as the telescopes own tracking would maintain alignment.  
> **username_2**: I was going to ask the same question, but with a high-altitude drone (or such) instead of a satellite. The satellite would need to avoid apparent motion relative to the stars, which would be difficult to impossible. The nearest I can imagine is a highly elliptical orbit with the apoapsis velocity equal to the ground velocity at the observatory. You'd need an array of such shade-satellites, and you'd have to move them all when switching to a new target.  

---

## 1 answers

### Answer by username_3 on 2017-08-10. Score: 6

If the starshade was to stay in place over the ground telescope, it would have to be in a geosynchronous orbit, which puts it almost 36,000 km from Earth's surface. To cover an angular distance of 1 arcsecond (1/3600 of a degree), it would have a size of around 10km. Certainly not impossible, but technologically impractical at the moment. Also, the starshade would only shade a small region of the sky, so it wouldn't be useful from other observing sites.

As for the space telescopes using a starshade in geosynchronous orbit; that would be impossible, at least for scopes orbiting Earth, like Hubble is. The starshade is orbiting Earth at a different distance, and therefore speed, than the telescopes. As far as I can see, it would be near impossible to keep them aligned for anything more than a few minutes. I haven't done any number-crunching on this, though.

> **Comments:**
> **username_0**: Maybe one can find two synchronized halo orbits at the Moon? A telescope in GEO is of course another solution, which allows for smaller star shade.  
> **username_4**: Winning answer! Except the starshade wouldn't have to cover an arcsecond. That would block the star's planets too, as well as the nearby stars. You'd only block the star itself which is ~ a milliarcsecond. So the occultor would only need to be 10 meters wide.  

---

