<p>This can best be described by two slides from <a href="http://www.iap.fr/microlensing2016/presentations/Geert-Barentsen.pdf" rel="nofollow noreferrer">this presentation</a>.</p>

<p>"Forward-facing" implies looking towards Earth in the spacecraft's orbit, in the direction of the spacecraft's velocity vector:</p>

<p><a href="https://i.sstatic.net/rY4SW.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/rY4SW.png" alt="enter image description here"></a></p>

<p>"Backward-facing" implies looking in the opposite direction, away from Earth and in the opposite direction to that of the spacecraft's velocity vector:</p>

<p><a href="https://i.sstatic.net/HnmSq.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/HnmSq.png" alt="enter image description here"></a></p>

<p>These are from the C9 campaign, which also used a forward-facing orientation.</p>

CC BY-SA 3.0
2016-09-14T16:59:00.637Z
Why does it matter though?  Can't you see the same stars from both places in the orbit?  In fact, I would guess that a "perpendicular facing", roughly pointing opposite from the sun, would provide the best viewing for ground telescopes, because then the relevant field of view would be highest in the sky around midnight.
NeutronStar
CC BY-SA 3.0
2016-09-14T17:03:20.633Z
@Joshua No, you won't be able to see the same stars. Remember that this is only for a small portion of an orbit (C9 was for a couple months, corresponding to a relatively small change in the orbit), and so the telescope needed to be pointed in a particular direction. In this case, the target superstamp was, in the graphs above, to the bottom (see Figure 6 [here](http://arxiv.org/pdf/1512.09142v2.pdf)).
HDE 226868
CC BY-SA 3.0
2016-09-14T17:27:15.203Z
I found the animations linked in the caption of that Figure most helpful.  So over the course of the campaign, the campaign direction transitions from being in the direction of Earth from the point of view of Kepler to being roughly opposite the sun for both Earth and Kepler.
NeutronStar
CC BY-SA 3.0
2016-09-14T19:50:09.057Z
You can see the same stars in backward facing if you wait 6 months.  The reason for switching to forward facing is to allow simultaneous observations from the Earth.  In backwards facing configuration, the K2 field of view sets very early in the evening, but in forward facing the K2 field is up for most of the night.  The downside to forward facing is that the Earth is in the K2 field for part of time and scattered light from this bright object may be a bit of a problem.
eshaya
CC BY-SA 3.0
2016-09-14T16:09:51.153Z
2016-09-14T16:09:51.153Z
HDE 226868
<p>I just noticed <a href="https://keplerscience.arc.nasa.gov/change-to-campaign-16-field-position-and-delay-to-go-cycle-5-deadline.html" rel="nofollow">this announcement</a> from the K2 mission that the field observed for Campaign 16 of the K2 mission would be changed so that the telescope would be "forward facing", saying that "observing in this mode allows for simultaneous observations from K2 and from Earth."</p>

<p>(an aside: Campaign 17 was originally planned to be a forward facing to facilitate supernova science, but it was discovered that the telescope may not have enough fuel to last through Campaign 17, hence the modification to Campaign 16 to still facilitate supernova science)</p>

<p>What exactly does it mean to be forward facing?</p>

<space-telescope><kepler><k2>
What does "forward facing" mean for space telescopes?
NeutronStar
# What does "forward facing" mean for space telescopes?

(Asked by: username_0 on 2016-09-14)

I just noticed [this announcement](https://keplerscience.arc.nasa.gov/change-to-campaign-16-field-position-and-delay-to-go-cycle-5-deadline.html) from the K2 mission that the field observed for Campaign 16 of the K2 mission would be changed so that the telescope would be "forward facing", saying that "observing in this mode allows for simultaneous observations from K2 and from Earth."

(an aside: Campaign 17 was originally planned to be a forward facing to facilitate supernova science, but it was discovered that the telescope may not have enough fuel to last through Campaign 17, hence the modification to Campaign 16 to still facilitate supernova science)

What exactly does it mean to be forward facing?

**Tags:** space-telescope, kepler, k2

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## 1 answers

### Answer by username_1 on 2016-09-14. Score: 4 | Accepted answer

This can best be described by two slides from [this presentation](http://www.iap.fr/microlensing2016/presentations/Geert-Barentsen.pdf).

"Forward-facing" implies looking towards Earth in the spacecraft's orbit, in the direction of the spacecraft's velocity vector:

[![enter image description here](https://i.sstatic.net/rY4SW.png)](https://i.sstatic.net/rY4SW.png)

"Backward-facing" implies looking in the opposite direction, away from Earth and in the opposite direction to that of the spacecraft's velocity vector:

[![enter image description here](https://i.sstatic.net/HnmSq.png)](https://i.sstatic.net/HnmSq.png)

These are from the C9 campaign, which also used a forward-facing orientation.

> **Comments:**
> **username_0**: Why does it matter though?  Can't you see the same stars from both places in the orbit?  In fact, I would guess that a "perpendicular facing", roughly pointing opposite from the sun, would provide the best viewing for ground telescopes, because then the relevant field of view would be highest in the sky around midnight.  
> **username_1**: @Joshua No, you won't be able to see the same stars. Remember that this is only for a small portion of an orbit (C9 was for a couple months, corresponding to a relatively small change in the orbit), and so the telescope needed to be pointed in a particular direction. In this case, the target superstamp was, in the graphs above, to the bottom (see Figure 6 [here](http://arxiv.org/pdf/1512.09142v2.pdf)).  
> **username_0**: I found the animations linked in the caption of that Figure most helpful.  So over the course of the campaign, the campaign direction transitions from being in the direction of Earth from the point of view of Kepler to being roughly opposite the sun for both Earth and Kepler.  
> **username_2**: You can see the same stars in backward facing if you wait 6 months.  The reason for switching to forward facing is to allow simultaneous observations from the Earth.  In backwards facing configuration, the K2 field of view sets very early in the evening, but in forward facing the K2 field is up for most of the night.  The downside to forward facing is that the Earth is in the K2 field for part of time and scattered light from this bright object may be a bit of a problem.  

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