EVM-2 Notice of Partnership Questions and Answers

January 23, 2015

Q1The NPO states "The imager(s) on each spacecraft shall create images covering a ground swath of +/- 576 km from nadir align the orbit track by +/-100 km across the orbit track from nadir". At 825 km orbit with 30m per pixel resolution at 8 bits per pixel, each image would be 1.8 Gbits = 216 Mbytes. This would produce approximately 43 Gbytes per orbit. It is not possible to downlink this much data. Is the requirement really 30 km per pixel? Or is the footprint of each image not as big? Or a combination thereof.

A1The pertinent GRC EVM-2 mission requirements from the Notice of Partnering Opportunity are as follows:

• The GRC EVM-2 mission shall consist of four spacecraft flying in formation in a Sun Synchronous low Earth orbit at approximately 825 km. altitude.

• Each spacecraft shall carry monochromatic imagers resolving the red light component of the visible spectrum (600-680 nm) at eight bit per pixel resolution.

• The images shall have a ground resolution of 30 meters/pixel.• The imager(s) on each spacecraft shall create images covering a ground swath of +/- 576 km from

nadir along the orbit track, and by +/-100 km across the orbit track measured from a line that is canted 15 degrees to the east from nadir.

• Imaging shall be done only when the spacecraft are in sunlight.

Potential partners may also consider the following:

• An image is required to be taken every 20 seconds• The orbit parameters are:

– Altitude = 824 km– Inclination = 98.7º– Period = 101 minutes– Local Time of Ascending Node = 13:30 hours +/- 10 minutes– The constellation of four spacecraft should have image overlap as shown below

A1 continued

• Potential partners should consider:• the amount of on-board data storage the spacecraft would require• the type of communications system and communications protocols necessary

to return this amount of data to the ground.• Ground network coverage requirements

Q2What role does GRC have in this?

A2

The NASA Glenn Research Center (GRC) is managing the Project, providing Systems Engineering and Integration (SE&I), Safety and Mission Assurance (S&MA) oversight, and contract oversight.

Q3What is the science that GRC is trying to accomplish and what heritage does GRC have in the science area?

A3

GRC is working with a team of scientists to determine the updraft velocity of clouds. While GRC does not have specific heritage in this particular science area we have a very strong science team from major universities with strong atmospheric science involvement.

This mission aligns with GRC strategic planning to align our flight systems experience to Earth Science missions, and a GRC scientist is supporting the science team.

Q4The GRC EVM-2 mission shall consist of four spacecraft flying in formation in a Sun Synchronous low Earth orbit at approximately 825 km. altitude.Questions:

1) Is there a required time of ascending node? 2) What is the nature of the formation desired? 3) For example, are all the satellites in the same orbit separated by true anomaly?

A4

See A1

Q5The spacecraft shall be capable of being launched in a ride-share configuration along with a primary spacecraft or by themselves on a single launch vehicle.The spacecraft shall have an operational life on-orbit of at least one year, commencing at the completion of on-orbit commissioning.Each spacecraft shall carry monochromatic imagers resolving the red light component of the visible spectrum (600-680 nm) at eight bit per pixel resolution.

Questions: What volume (configuration), mass, and power should SC vendors assume for each imager in preparing responses?

A5

The budget constraints imposed by an EV class mission combined with the NOP requirements of launching four spacecraft on a single launch vehicle, or in a ride share configuration with a larger spacecraft will drive the size of the spacecraft, which will, in turn, drive the configuration of the imager(s).

Q6 Do the data have a latency requirement for downlinking?

A6

At this time there is no latency requirement, but such a requirement may evolve during proposal writing.

Q7The images shall have a ground resolution of 30 meters/pixel.The imager(s) on each spacecraft shall create images covering a ground swath of +/- 576 km from nadir along the orbit track by +/-100 km across the orbit track from nadir. What is the SC pointing control and jitter requirement?The imager(s) on each spacecraft shall have a cant angle of 15 degree measure eastward from nadir.

Questions: Is 30m resolution required at nadir or the furthest extent of the swath?

A7 The 30m resolution pertains to each pixel in the image, irrespective of it being at nadir or at the periphery of

the image. We do require ideally 30 m resolution at all ranges. But practically we can have 30 m resolution at the longest ranges, and respectively higher resolution at the shorter ranges. With the current swath area , there would be a bow tie effect, which will widen the nominal 200 km at the furthest range to much more than at the shortest range. We can accommodate this if the nominal width is 200 km at the furthest range. Ideally, we can have a camera with better pixel resolution and field of view, that will collate adjacent pixels at the shorter range to keep the nominal resolution nearly constant.Options and issues regarding this requirement should be discussed in the response to the NOP.

Q8 Is there a jitter requirement?

A8

Not at this time, but one will evolve during proposal preparation based on the spacecraft systems.

Q9 Are there pointing or knowledge requirements?

A9

Not at this time, but one will evolve during proposal preparation based on the spacecraft systems.

Q10Can you explain how to interpret the requirement to image +/- 100 km across the orbit track along with the requirement for the imager(s) to be canted 15 degrees eastward of nadir?

A10

Q11Must the entire swath be imaged at all times or is a scanning mechanism acceptable?

A11See the Answer to Q19

Q12 Please confirm the due date for the responses to this notice is Feb, 3, 2015.

A12

Confirmed.

Q13Is the cost cap for Earth Venture Mission-2 the same as before (i.e., $150M) and does the cap include spacecraft, instrument, launch and all science team support?

A13

The Earth Venture Mission-2 Announcement of Opportunity has not been posted.

Q14In section 2 – Overview it is stated: Based on the responses to this Notice, GRC anticipates selecting one or multiple instrument suppliers and a single spacecraft vendor with which GRC would then immediately work directly with in development of the GRC EVM-2 mission.

o Can the instrument supplier and the spacecraft be one and the same?o Are you looking for instrument designs as well as spacecraft designs?

A14

Yes.Yes.

Q15In the EARTH VENTURE SPACECRAFT section it is stated: The GRC EVM-2 mission shall consist of four spacecraft flying in formation in a Sun Synchronous low Earth orbit. Can you provide more details of the formation, e.g.:

Will the spacecraft be required to maintain a given position with respect to each other that might require fuel to maintain that position?

A15

The spacecraft should be maintained 80 seconds apart in the orbital arc.

Q16Will the spacecraft be dispersed around the same sun synchronous orbit with the same crossing time?

A16

The LTAN (Local Time of Ascending Node) crossing time should be assumed to be at the center of the constellation.

Q17How accurately does that crossing time have to be maintained?

A17

See the answer to Q1.

Q18There are very few details provided of the imagers that the spacecraft will have to carry. Is it your intention that the responders will provide estimates of the size, weight and power of imagers that can meet the performance requirements stated and hence deduce the size of spacecraft required to accommodate them?

A18

Yes

Q19In the EARTH VENTURE SPACECRAFT section it is stated: The imager(s) on each spacecraft shall create images covering a ground swath of +/- 576 km from nadir along the orbit track by +/-100 km across the orbit track from nadir.Does this requirement imply that the 200 km x 1152 km image is captured simultaneously or can the along track +/-576 km image be built up using the motion of the spacecraft like a conventional pushbroom imager?

A19

A pushbroom imager could be acceptable only if the entire swath area (in-track and cross-track) could be scanned in 2 seconds. While longer scan times of up to 10 seconds might be acceptable, the in-track swath dimension would have to be increased to compensate for the spacecraft movement during that time. The precise amount would have to be calculated. This could be assessed during proposal development.

Q20To size the onboard data recorder we need to know the CONOPS such as how many such images are collected before the opportunity to downlink the data and where the downlink stations are assumed to be. Will this information be provided?

A20

Downlink should be assumed to NASA communications assets in the Near Earth Network or the Space Network.

Q21In the EARTH VENTURE SPACECRAFT section it is stated: The imager(s) on each spacecraft shall have a cant angle of 15 degree measure eastward from nadir.Does this requirement mean that the +/-100 km swath across the orbit track is across the orbit track that is 15 degrees off nadir?

A21

The cross track swath is +/- 100 km measure from a center line that is canted eastward from nadir by 15 degrees. See the figure associated with the answer to Q10.