<p>Currently New Horizions is temporarily hibernating; it's last activity was two months ago. So I'm going to post a supplementary answer here because it is &quot;operational&quot; in the sense that it still works and will be used again, even though it is not &quot;active&quot; at the moment.</p>
<hr />
<p>The most recent and farthest-from-earth telescopic observations that I know of are from the <a href="https://en.wikipedia.org/wiki/New_Horizons" rel="noreferrer">New Horizons</a> spacecraft and it's <a href="https://en.wikipedia.org/wiki/New_Horizons#Long-Range_Reconnaissance_Imager_(LORRI)" rel="noreferrer">Long-Range Reconnaissance Imager</a> (LORRI), a 208 mm (8.2 inch) diameter Ritchey–Chretien telescope equipped with silicon-carbide optics and a cooled silicon CCD imager with a resolution of about 1 arcsecond:</p>
<blockquote>
<p>The Long-Range Reconnaissance Imager (LORRI) is a long-focal-length imager designed for high resolution and responsivity at visible wavelengths. The instrument is equipped with a 1024×1024 pixel by 12-bits-per-pixel monochromatic CCD imager giving a resolution of 5 μrad (~1 arcsec)] The CCD is chilled far below freezing by a passive radiator on the antisolar face of the spacecraft. This temperature differential requires insulation, and isolation from the rest of the structure. The 208.3 mm (8.20 in) aperture <a href="https://en.wikipedia.org/wiki/Ritchey-Chr%C3%A9tien_telescope" rel="noreferrer">Ritchey–Chretien</a> mirrors and metering structure are made of silicon carbide, to boost stiffness, reduce weight, and prevent warping at low temperatures. The optical elements sit in a composite light shield, and mount with titanium and fiberglass for thermal isolation. Overall mass is 8.6 kg (19 lb), with the optical tube assembly (OTA) weighing about 5.6 kg (12 lb), for one of the largest silicon-carbide telescopes flown at the time (now surpassed by Herschel).</p>
</blockquote>
<p>In December 2017 LORRI captured the images below of two Kuiper belt objects. From the February 9, 2018 NASA News item <a href="https://www.nasa.gov/feature/new-horizons-captures-record-breaking-images-in-the-kuiper-belt" rel="noreferrer">New Horizons Captures Record-Breaking Images in the Kuiper Belt</a>:</p>
<blockquote>
<p>NASA’s New Horizons spacecraft recently turned its telescopic camera toward a field of stars, snapped an image – and made history.</p>
<p>The routine calibration frame of the “Wishing Well” galactic open star cluster, made by the Long Range Reconnaissance Imager (LORRI) on Dec. 5, was taken when New Horizons was 3.79 billion miles (6.12 billion kilometers, or 40.9 astronomical units) from Earth – making it, for a time, the farthest image ever made from Earth.</p>
<p>New Horizons was even farther from home than NASA’s Voyager 1 when it captured the famous “Pale Blue Dot” image of Earth. That picture was part of a composite of 60 images looking back at the solar system, on Feb. 14, 1990, when Voyager was 3.75 billion miles (6.06 billion kilometers, or about 40.5 astronomical units [AU]) from Earth. Voyager 1’s cameras were turned off shortly after that portrait, leaving its distance record unchallenged for more than 27 years.</p>
<p>LORRI broke its own record just two hours later with images of Kuiper Belt objects 2012 HZ84 and 2012 HE85 – further demonstrating how nothing stands still when you’re covering more than 700,000 miles (1.1 million kilometers) of space each day.</p>
</blockquote>
<p>Here is a 25-Feb-2018 screen shot of a map of the Solar System with New Horizon's current position plotted. You can read more about New Horizons at:</p>
<ul>
<li><p><a href="http://pluto.jhuapl.edu/Mission/Where-is-New-Horizons/index.php" rel="noreferrer">Where is New Horizons</a></p>
</li>
<li><p><a href="https://www.nasa.gov/mission_pages/newhorizons/main/index.html" rel="noreferrer">NASA's New Horizons main page</a></p>
</li>
</ul>
<p><a href="https://i.sstatic.net/9sMOm.jpg" rel="noreferrer"><img src="https://i.sstatic.net/9sMOm.jpg" alt="New Horizons position Feb. 2018" /></a></p>
<hr />
<p>Instrumentation on New Horizons is extensively described/explained in Spaceflight 101's <a href="http://spaceflight101.com/newhorizons/instrument-overview/" rel="noreferrer">Instrument Overview</a>.</p>
<p>The LORRI telescope is described for example in the ArXiv preprint <a href="https://arxiv.org/abs/0709.4278" rel="noreferrer">Long-Range Reconnaissance Imager on New Horizons</a> (click &quot;PDF&quot;). It has a spectral range of about 350 to 850 nm. The limiting magnitude for high precision positional measurements is about +11.5 for a short exposure, but with some binning and a roughly 10 second exposure that increases to about +17:</p>
<blockquote>
<p>For optical navigation, LORRI is required to be able to image a star of visual magnitude V=11.5 at SNR&gt;7 in a single 100 ms exposure, with full width at half maximum (FWHM) &gt;1 pixel. It is not desirable for too great a fraction of the energy from a point source to be imaged onto a single pixel, because stellar images become too undersampled. LORRI has a 4×4 pixel binning mode, for which its limiting magnitude requirement is V&gt;17 in a single exposure of 9.9 s. This 4×4 pixel-binning mode will be used to search for the target KBO and to perform optical navigation on approach.</p>
</blockquote>
<p><a href="https://i.sstatic.net/PKujo.png" rel="noreferrer"><img src="https://i.sstatic.net/PKujo.png" alt="New Horizon's Long Range Imager LORRI" /></a></p>
<hr />
<p><strong>below:</strong> Image and caption from <a href="https://www.nasa.gov/feature/new-horizons-captures-record-breaking-images-in-the-kuiper-belt" rel="noreferrer">here</a>:</p>
<blockquote>
<p>With its Long Range Reconnaissance Imager (LORRI), New Horizons has observed several Kuiper Belt objects (KBOs) and dwarf planets at unique phase angles, as well as Centaurs at extremely high phase angles to search for forward-scattering rings or dust. These December 2017 false-color images of KBOs 2012 HZ84 (left) and 2012 HE85 are, for now, the farthest from Earth ever captured by a spacecraft. They're also the closest-ever images of Kuiper Belt objects.</p>
</blockquote>
<p><a href="https://i.sstatic.net/L41HN.jpg" rel="noreferrer"><img src="https://i.sstatic.net/L41HN.jpg" alt="KBO objects imaged by New Horizons" /></a></p>

CC BY-SA 3.0
2018-02-25T03:58:42.407Z
Could it observe quasars, or does it not have the necessary equipment or conditions for that?
Euphorbium
CC BY-SA 3.0
2018-02-25T04:29:23.657Z
@Euphorbium Hmm... it would depend the object's brightness, and what it is in particular you'd want to observe. I will see what I can find out about LORRI's limiting magnitude.
uhoh
CC BY-SA 3.0
2018-02-25T04:43:45.190Z
@Euphorbium I've added a link and a bit of information about the telescope itself and limiting magnitude. For very distant objects well beyond the solar system, you can think of LORRI roughly as an 8-inch telescope with a cooled CCD above Earth's atmosphere, with a very, very, very, slowwwww data stream back to Earth.
uhoh
CC BY-SA 3.0
2018-02-25T07:31:14.257Z
This would be about the worst telescope to use for looking at quasars. The brightest quasar is mag 12.5. It could see it, but there is nothing it could do with it.
James K
CC BY-SA 3.0
2018-02-25T07:44:24.790Z
@JamesK and the Kuiper belt, with a data link of (guessing) 100 bits per second back to Earth is not  a good place to put it either. Luckily, the question is not about quasars!
uhoh
CC BY-SA 3.0
2018-02-26T20:37:33.200Z
Wait a minute - is New Horizons really a "space telescope" or just a spaceship (that, of course, like all spaceships, has a few telescopes on board?)  If we allow New Horizons, might as well just say Voyager etc.?
Fattie
CC BY-SA 3.0
2018-02-27T00:14:02.287Z
@Fattie there is no need to wait, not even for a minute. A careful read of the answer would have shown you that LORRI is indeed a telescope in active use for astrometry. It is physically far closer to some of these KBO's than Earth is, and since we have an extremely precise fix on the telescope's location, this provides data on these objects that could not be obtained from Earth. A 21 cm Ritchey–Chretien telescope equipped with a cooled silicon CCD imager with a resolution of about 1 arcsecond in active use for astrometry, in space, is indeed a "space telescope" without question.
uhoh
CC BY-SA 3.0
2018-02-27T00:22:36.857Z
Awesome!  I heart space telescopes.
Fattie
CC BY-SA 3.0
2018-02-27T00:23:17.243Z
@Fattie the unique data includes both triangulation of positions via the unique location of the telescope, as well as photometry *and imaging* of the KBO's at oblique illumination phase angles very different from what is available from Earth which is so close to the Sun. "With its Long Range Reconnaissance Imager (LORRI), New Horizons has observed several Kuiper Belt objects (KBOs) and dwarf planets at unique phase angles, as well as Centaurs at extremely high phase angles to search for forward-scattering rings or dust."
uhoh
CC BY-SA 3.0
2018-02-25T03:49:21.177Z
2018-02-25T05:32:03.357Z
2020-06-17T09:47:40.653Z
uhoh
<p>From the earth, and from the sun. Only interested in active, operational ones.</p>

CC BY-SA 3.0
2018-02-26T15:29:04.060Z
I'm tempted to get snarky and suggest a few over in the Crab Nebula, but most likely you meant telescopes built on Earth :-)
Carl Witthoft
CC BY-SA 3.0
2018-02-26T20:36:36.357Z
Is it true that ALL space telescopes are either (a) in orbit (b) at L2-ish or (c) the only exception is New Horizons??
Fattie
<telescope><space><space-telescope>
Which space telescope is the most distant?
Euphorbium
# Which space telescope is the most distant?

(Asked by: username_0 on 2018-02-25)

From the earth, and from the sun. Only interested in active, operational ones.

**Tags:** telescope, space, space-telescope
> **Comments:**
> **username_1**: I'm tempted to get snarky and suggest a few over in the Crab Nebula, but most likely you meant telescopes built on Earth :-)  
> **username_2**: Is it true that ALL space telescopes are either (a) in orbit (b) at L2-ish or (c) the only exception is New Horizons??  

---

## 1 answers

### Answer by username_3 on 2018-02-25. Score: 10 | Accepted answer

Currently New Horizions is temporarily hibernating; it's last activity was two months ago. So I'm going to post a supplementary answer here because it is "operational" in the sense that it still works and will be used again, even though it is not "active" at the moment.

---

The most recent and farthest-from-earth telescopic observations that I know of are from the [New Horizons](https://en.wikipedia.org/wiki/New_Horizons) spacecraft and it's [Long-Range Reconnaissance Imager](https://en.wikipedia.org/wiki/New_Horizons#Long-Range_Reconnaissance_Imager_(LORRI)) (LORRI), a 208 mm (8.2 inch) diameter Ritchey–Chretien telescope equipped with silicon-carbide optics and a cooled silicon CCD imager with a resolution of about 1 arcsecond:

> The Long-Range Reconnaissance Imager (LORRI) is a long-focal-length imager designed for high resolution and responsivity at visible wavelengths. The instrument is equipped with a 1024×1024 pixel by 12-bits-per-pixel monochromatic CCD imager giving a resolution of 5 μrad (~1 arcsec)] The CCD is chilled far below freezing by a passive radiator on the antisolar face of the spacecraft. This temperature differential requires insulation, and isolation from the rest of the structure. The 208.3 mm (8.20 in) aperture [Ritchey–Chretien](https://en.wikipedia.org/wiki/Ritchey-Chr%C3%A9tien_telescope) mirrors and metering structure are made of silicon carbide, to boost stiffness, reduce weight, and prevent warping at low temperatures. The optical elements sit in a composite light shield, and mount with titanium and fiberglass for thermal isolation. Overall mass is 8.6 kg (19 lb), with the optical tube assembly (OTA) weighing about 5.6 kg (12 lb), for one of the largest silicon-carbide telescopes flown at the time (now surpassed by Herschel).

In December 2017 LORRI captured the images below of two Kuiper belt objects. From the February 9, 2018 NASA News item [New Horizons Captures Record-Breaking Images in the Kuiper Belt](https://www.nasa.gov/feature/new-horizons-captures-record-breaking-images-in-the-kuiper-belt):

> NASA’s New Horizons spacecraft recently turned its telescopic camera toward a field of stars, snapped an image – and made history.
>
> The routine calibration frame of the “Wishing Well” galactic open star cluster, made by the Long Range Reconnaissance Imager (LORRI) on Dec. 5, was taken when New Horizons was 3.79 billion miles (6.12 billion kilometers, or 40.9 astronomical units) from Earth – making it, for a time, the farthest image ever made from Earth.
>
> New Horizons was even farther from home than NASA’s Voyager 1 when it captured the famous “Pale Blue Dot” image of Earth. That picture was part of a composite of 60 images looking back at the solar system, on Feb. 14, 1990, when Voyager was 3.75 billion miles (6.06 billion kilometers, or about 40.5 astronomical units [AU]) from Earth. Voyager 1’s cameras were turned off shortly after that portrait, leaving its distance record unchallenged for more than 27 years.
>
> LORRI broke its own record just two hours later with images of Kuiper Belt objects 2012 HZ84 and 2012 HE85 – further demonstrating how nothing stands still when you’re covering more than 700,000 miles (1.1 million kilometers) of space each day.

Here is a 25-Feb-2018 screen shot of a map of the Solar System with New Horizon's current position plotted. You can read more about New Horizons at:

* [Where is New Horizons](http://pluto.jhuapl.edu/Mission/Where-is-New-Horizons/index.php)
* [NASA's New Horizons main page](https://www.nasa.gov/mission_pages/newhorizons/main/index.html)

[![New Horizons position Feb. 2018](https://i.sstatic.net/9sMOm.jpg)](https://i.sstatic.net/9sMOm.jpg)

---

Instrumentation on New Horizons is extensively described/explained in Spaceflight 101's [Instrument Overview](http://spaceflight101.com/newhorizons/instrument-overview/).

The LORRI telescope is described for example in the ArXiv preprint [Long-Range Reconnaissance Imager on New Horizons](https://arxiv.org/abs/0709.4278) (click "PDF"). It has a spectral range of about 350 to 850 nm. The limiting magnitude for high precision positional measurements is about +11.5 for a short exposure, but with some binning and a roughly 10 second exposure that increases to about +17:

> For optical navigation, LORRI is required to be able to image a star of visual magnitude V=11.5 at SNR>7 in a single 100 ms exposure, with full width at half maximum (FWHM) >1 pixel. It is not desirable for too great a fraction of the energy from a point source to be imaged onto a single pixel, because stellar images become too undersampled. LORRI has a 4×4 pixel binning mode, for which its limiting magnitude requirement is V>17 in a single exposure of 9.9 s. This 4×4 pixel-binning mode will be used to search for the target KBO and to perform optical navigation on approach.

[![New Horizon's Long Range Imager LORRI](https://i.sstatic.net/PKujo.png)](https://i.sstatic.net/PKujo.png)

---

**below:** Image and caption from [here](https://www.nasa.gov/feature/new-horizons-captures-record-breaking-images-in-the-kuiper-belt):

> With its Long Range Reconnaissance Imager (LORRI), New Horizons has observed several Kuiper Belt objects (KBOs) and dwarf planets at unique phase angles, as well as Centaurs at extremely high phase angles to search for forward-scattering rings or dust. These December 2017 false-color images of KBOs 2012 HZ84 (left) and 2012 HE85 are, for now, the farthest from Earth ever captured by a spacecraft. They're also the closest-ever images of Kuiper Belt objects.

[![KBO objects imaged by New Horizons](https://i.sstatic.net/L41HN.jpg)](https://i.sstatic.net/L41HN.jpg)

> **Comments:**
> **username_0**: Could it observe quasars, or does it not have the necessary equipment or conditions for that?  
> **username_3**: @Euphorbium Hmm... it would depend the object's brightness, and what it is in particular you'd want to observe. I will see what I can find out about LORRI's limiting magnitude.  
> **username_3**: @Euphorbium I've added a link and a bit of information about the telescope itself and limiting magnitude. For very distant objects well beyond the solar system, you can think of LORRI roughly as an 8-inch telescope with a cooled CCD above Earth's atmosphere, with a very, very, very, slowwwww data stream back to Earth.  
> **username_4**: This would be about the worst telescope to use for looking at quasars. The brightest quasar is mag 12.5. It could see it, but there is nothing it could do with it.  
> **username_3**: @JamesK and the Kuiper belt, with a data link of (guessing) 100 bits per second back to Earth is not  a good place to put it either. Luckily, the question is not about quasars!  
> **username_2**: Wait a minute - is New Horizons really a "space telescope" or just a spaceship (that, of course, like all spaceships, has a few telescopes on board?)  If we allow New Horizons, might as well just say Voyager etc.?  
> **username_3**: @Fattie there is no need to wait, not even for a minute. A careful read of the answer would have shown you that LORRI is indeed a telescope in active use for astrometry. It is physically far closer to some of these KBO's than Earth is, and since we have an extremely precise fix on the telescope's location, this provides data on these objects that could not be obtained from Earth. A 21 cm Ritchey–Chretien telescope equipped with a cooled silicon CCD imager with a resolution of about 1 arcsecond in active use for astrometry, in space, is indeed a "space telescope" without question.  
> **username_2**: Awesome!  I heart space telescopes.  
> **username_3**: @Fattie the unique data includes both triangulation of positions via the unique location of the telescope, as well as photometry *and imaging* of the KBO's at oblique illumination phase angles very different from what is available from Earth which is so close to the Sun. "With its Long Range Reconnaissance Imager (LORRI), New Horizons has observed several Kuiper Belt objects (KBOs) and dwarf planets at unique phase angles, as well as Centaurs at extremely high phase angles to search for forward-scattering rings or dust."  

---

