Hi Justin & Arnold,
I completely agree with the stray light concern and it was a concern I
raised with Houman as well.
In an ideal world we'd be able to stick the aperture of the integrating
sphere right out of the side of the spacecraft so that there's no chance
of the sphere's light reflecting off anything. Unfortunately with the
sphere being as small as it is and with the large connectors coming off
of the front hemisphere, it's not possible to get it that close to the
outside surface. The small size of the sphere is also making it
impractical to put the LEDs anywhere except the exit aperture; also
non-ideal.
These difficulties and non-idealities are all pointing to the sphere
being undersized, at least on the nanosatellite (it may be perfectly
sized for the balloon experiments). Unfortunately the current
incantation of the spacecraft cannot accommodate a larger sphere.
The obvious solution is to use a bigger spacecraft. Our NEMO-15kg bus
(the next size up) could probably house a 6" sphere and make most of
these problems go away. Finding room for radiators, antennas, etc. would
also become much easier. Note, because the payload would be largely
empty space, we probably wouldn't even come close to hitting the 15kg
mark either so the mass (launch cost) penalty would not be as extreme as
it might appear.
I think it's too late to change the baseline for the FAST program, but
in the final report we should probably make note of these non-idealities
and, when pursuing funding for the flight system, budget enough money
for the larger spacecraft (the cost delta is typically not that great).
Finally, for your interest, on projects requiring very black surfaces we
now use coatings such as the ones offered by n-Science.
http://www.nscicorp.org/deep_space_black.html
When I first looked into a baffle coated with this stuff I realized I
had never actually seen black before, only shades of dark grey.
Cheers,
Cordell
On 5/8/2015 1:59 PM, Justin Albert wrote:
> Houman and Cordell -- extremely good points from Arnold below.
>
> BTW, Arnold, you did the exactly right thing in cc'ing
> nanosat-hn-pa@projectaltair.org , so it should have ended up posted
> there, but it didn't! Did you get a bounce-back message by any
> chance, or did that cc just disappear?
>
> On Fri, 8 May 2015, Gaertner, Arnold wrote:
>> Hi Justin and Houman,
>> Thanks for forwarding the links.
>> The design looks interesting.
>> I have one comment:
>> The integrating sphere will emit light in all directions, not only in
>> the cone direction for which we provide unobstructed view of the
>> sphere port.
>> Be careful that none, or as little as possible (within the
>> uncertainty we require), of the light that is emitted outside this
>> angle and hits the PCB, or even the cone walls, does not get
>> scattered back into the direction of our view.
>> The cone black is never really black, and if it gets dust on it will
>> become a 'diffuse' scatterer.
>> The edges of the PCB will scatter.
>> Best regards,
>> Arnold
>>
>> -----Original Message-----
>> From: Justin Albert [mailto:jalbert@uvic.ca]
>> Sent: Thursday, May 07, 2015 23:24
>> To: nanosat-hn-pa@projectaltair.org
>> Subject: [ALTAIR] - some images (fwd)
>>
>>
>> *** Discussion title: ALTAIR Nanosat (STARCaL)
>>
>> At the bottom of this message are links to the drawings from Houman
>> (solid model renderings of the optical payload) which we discussed
>> during today's telecon.
>>
>> ---------- Forwarded message ----------
>> Date: Thu, 07 May 2015 13:03:33 -0400
>> From: Houman Hakima <hhakima@utias-sfl.net>
>> To: jalbert@uvic.ca, Cordell Grant <cgrant@utias-sfl.net>
>> Subject: [ALTAIR] - some images
>>
>> Hi Justin,
>>
>> Here are some images reflecting the changes that I have made since
>> last telecon. The most significant one would be the PCB that is
>> mounted around the output port and has 6 LEDs on it. I made sure that
>> the connectors, PCB and all the other components stay away from the
>> sphere's 60-deg cone.
>>
>> -- figures captions
>> fig 1: Overall view of the current payload design fig 2: wires can be
>> bundled. On the payload PCB same connector that is used for the
>> multi-colour laser can be used for the 6 LEDS.
>> fig 3: how LED board sits around the output port fig 4: the LEDs and
>> their PCB fit inside the integration sphere's baffle.
>> fig 5: Turret connectors do not intersect with the cone.
>>
>> Thanks,
>> Houman
>>
>> Attachment:
>> http://projectaltair.org/HyperNews/get/AUX/2015/05/07/20.19-59426-1.jpg
>> http://projectaltair.org/HyperNews/get/AUX/2015/05/07/20.19-41191-2.jpg
>> http://projectaltair.org/HyperNews/get/AUX/2015/05/07/20.19-94534-3.jpg
>> http://projectaltair.org/HyperNews/get/AUX/2015/05/07/20.19-95051-4.jpg
>> http://projectaltair.org/HyperNews/get/AUX/2015/05/07/20.19-86046-5.jpg
>>
>> -------------------------------------------------------------
>> Visit this projectALTAIR.org message (to reply or unsubscribe) at:
>> http://projectaltair.org/HyperNews/get/nanosat/7.html
>>
>
--
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* Cordell Grant, M.A.Sc.
* Manager, Satellite Systems
* Space Flight Laboratory
*
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