Initial specifications and requirements for mission and the satellite bus
| Parameter | Requirements | Justification/clarification | Status |
|---|---|---|---|
| Scientific | |||
| Purpose | Observe ocean color high resolution (at best effort), on order to "zoom in" on areas of interest identified by scientists. Target area will change wrt. time of year, occurring phenomena and so on. | Firm | |
| Area of interest | Details of plumes of (harmful) algal blooms | Firm | |
| Mission and payload | |||
| Observation/subject | Algae blooms | Firm | |
| Observation location | Norwegian waters, other targets of opertunity | Clarification needed: If coastal area/fjords are to be observed, how will this impact image quality? Will land pixels impact/destroy data | Firm |
| Size of area | 30 x 30 km^2 | Firm but may have longer in x-direction | |
| Instrument | HSI | 400-800 nm usable spectral range, 10-100 bands taken | Firm |
FoV | The orbit altitude can range from 400 - 600 km. More likely to be at 450-550 km. FoV will be 30 km at 500 km. | Firm | |
| Resolution (spacial, time, spectral) | The orbit altitude can range from 450 - 550 km. 250 m x 52 m spatial resolution at 500 km Minimum daily revisit, preferably 2 or 3 passes. 1 direct overhead pass is minimum. Technical: Depends on image data quality from slant rages. Not feasible for imaging at high slant, but still TBD from analysis (UAV etc.). Theoretically it is bad. Operational: Depends on cloud coverage and slant. | Firm, but not for cross-track viewing. | |
| Instrument properties | Sensitivity Number of photons SNR
| These numbers are TBC. Theoretical SNR<200 (practically worse). Photon count is something, but not much in NIR range. (3100 photons at 550 nm). Supported by data from oceanography, atmosphere physics and physical instrument properties. | In progress |
| Instrument maturity | Instrument tested and operation verified by using UAV, baloons, aircraft. | Work remains. Processing of data from UAV experiments remains in order to show proof-of-concept | TBC |
| Mechanical subsystem | |||
| Space craft size | 3U CubeSat (assumed) | Initial calculations indicate that 3U should provide enough room and power. May expand up to 6U if more power is needed, but 3U is good baseline. Open for other form factors if needed to meet specs. and cost. | Firm |
| Deployables | Antennas? Solar panels | Preferrable none. Depends on power reqs. | TBC |
| Payload physical envelope | Approx. 160 cm3 | Based on current model for UAVs. HSI ver. 4 | Reasonable estimate |
| Payload mass | 152 g (<500 g) | Based on current model for UAVs. HSI ver.4 | Reasonable estimate |
| Camera aperture placement | Zenith panel S-mount and C-mount | Reasonable estimate | |
| Payload material properties | Material type Thermal expansion of material The camera sensitivity wrt. thermal expansion, vibration and other disturbances | TBC. PEEK? Other advanced plastics? The satellite and payload will most likely experience large thermal gradients every pass. Data (informal) from other missions suggests that we can expect +20 C during sun illumination and -20 C during eclipse. The needed orbit will have around 30 min eclipse for every pass. Terminators are of interest with gradients of 20 deg/s Simulations must be performed and material must be determined (Youngs modulus, elasticity and fatigue correlation factor). Need to determine what material is best. Tolerances on lenses is important (focal length and aperture for each lens in mm, um or nm if necessary). Then we can test after FEA simulations. Prof. Echetermeyer may help on this. | In progress |
| Power subsystem | |||
| Payload energy consumption | 3 W for 3 minutes observation pr. pass | Estimation. Target observation time expected to be shorter than 3 minutes. More likely 54 seconds due to 20 deg viewing angle required for observable target. | Reasonable estimate |
| Peak power needed | 8-10 W | Should be able to operate TM/TC, downlink radio, ADCS and payload at once during target pass. | Reasonable estimate |
| Energy needed | Should be able to perform target observation (inkl. slewing maneuvering) and downlink for three consecutive passes | TBC | |
| Communications | |||
| Downlink data rate (usable bits) | Minimum: 200 kbit/s ok Request: 1 - 2 Mbit | Estimation of size of one target measurement packet, one pr. pass: Compressed (spectral domain) S-band: X-band: 18 Mbits / 10 Mbits/sec = 1.8 s Uncompressed: 500 pixels x 600 pixels x 12 bits/pixel x 100 channels = 360 Mbits S-band: X-band: 360 Mbits / 10 Mbits/sec = 36 s Attitude log information: 100 Hz gives additional 1-2 MB | Reasonable estimate |
| Downlink frequency band | 2200-2290 MHz (S-band) 8025-8400 MHz (X-band) | Used for non-commercial services. Information from NRS. TBC. Must clarify which kind of license is needed. Alternative? Must initiate frequency allocation process. Perhaps enough UHF/VHF downlink in consecutive passes (enable storing images - also raw) | TBC |
| Downlink power/EIRP needed | Depending on GS antenna size, power available and freq. band | TBC | |
| Downlink radio energy consumption | Ground station pass expected to be 3 < t < 11 min. Max 11 min in good pass depending on orbit type (800 km). Max 8.43 min in good pass on SSO and 600 km altitude - minimum 3.33 min on 1st and 3rd pass. One downlink pass pr. target observation. 3 day revisits achievable for SSO (6 in one day), 6 day revisits with 75 deg 800 km LEO. This based on Elev. angle = 10 deg for GS. | TBC | |
| Ground station/data access | Depending on frequency band If possible, GS at NTNU, in addition to others | TBC | |
| Launch and orbit | |||
| Orbit type |
SSO with good light conditions | Target area is far north --> ground stations expected to be far north. Backed by scientific needs: Target of observations must be well illuminated, since the algae blooms thrive in sunlight. | Firm, due to scientific needs.
|
| Orbit height | 400 - 600 km, 500 to be sought after | Low orbit preferable due to better resolution, higher gives longer GS pass | Firm, due to availability of launches. |
| Orbit inclination | 75-98 deg | Referred to orbit type, probably SSO | |
| Other parameters | Ω: 80 - 110 deg or Ω: 270 - 300 deg
| Pass should give good light conditions over target area during summer. North-south might also lead to sun glare due to slew maneuver (when looking back) but not when passing and viewing away from sun behind (at high latitudes - checked this). | Reqs. firm, availability TBC |
| ADCS | |||
| Slewrate (max, precision) | Minimum: 0.5 deg/s Request: 1 deg/s | In order to be able to point towards target during a pass 1 deg/s seem to be resonable (after simulations). This needs to be matched with exposure time which also is a trade-off for spatial resolution and SNR. | Firm |
| Pointing accuracy | 1 deg, 0.1 deg (0.01 deg) | The higher the better, although (payload pointing) requirements may set it to even higher pointing accuracy requirement. Potential need for high (relative) accuracy during slew operation. | Firm |
| Angle requirement | Longitudinal: Max. 20 deg from Nadir. Latitudinal: Max. 64 deg from Nadir, min 45 deg from Nadir | Longitudinal requirement due to better GSD achievement
Latitudinal requirement due to observation of target on next pass (due to Earth rotation), since target has moved 1200 km in next pass. | Firm |
| Momentum budget | Satellite must be able to perform slewing maneuver for four consecutive passes. 26Wh pass 1 (image and downlink) -> 14 Wh pass 2 (image and downlink) -> pass 3 images cannot be downlinked (not enough power). Max solar power in: 9 W Avg. solar power in: 4.3 W Min solar power in: 2.2 W Capacity: 26 Wh (38 Wh w/o discharge effects) | Not if 3 other passes are bad. | |
| Peak power needed during slew | 30 W for 2 min (OK) | ||
| Satellite position knowledge | <10 m |