Each Sapling mission to date has had an ODAR generated with NASA DAS 3.2.2 and written in accordance with NASA-STD-8719.14 and FCC § 97.207. The ODAR is a requirement to secure FCC licensing and guarantees that the spacecraft achieves top level requirement SYS-502. The table below lists requirements as they appear in NASA-STD-8719.14, including only those that apply to the Sapling spacecraft. Sapling is compliant with all ODAR requirements and the complete ODAR for each mission is publicly available online through the FCC.
There is no debris released during normal operations of any Sapling spacecraft. This includes deployment mechanisms. Sapling uses fishing line to constrain its deployable tapespring antennas; deployment is triggered by a nichrome burn wire, and the fishing line segments are tied such that they remain attached to the tape springs after deployment, rather than separating from the spacecraft. The risk of spacecraft breakup due to accidental explosion is also very low. The only potential cause of accidental explosion is energy release from onboard batteries. As discussed in the EPS section of this document, the Panasonic NCR18650B cells and Sapling Seedpod battery board are designed and selected for a low risk of battery failure.
The risk of on-orbit collision with large debris, as calculated using NASA DAS, was found to be 1.969 x 10-7. Large debris are classified as any RSO larger than 10 cm in diameter. The probability of accidental collision with small objects (including orbital debris and meteoroids) was also assessed using NASA DAS. The likelihood of such a collision preventing compliance with post mission disposal requirements was found to be less than 0.01.
Sapling Giganteum will be disposed of via uncontrolled atmospheric reentry, and is expected to remain in orbit for 4.485 years total. Probability of successful atmospheric disposal is 0.999 and within 5 years of launch (as per the FCC’s updated lifetime restrictions). No component of the spacecraft will survive atmospheric reentry and impact the surface of the Earth with kinetic energy in excess of 15 joules. The calculated casualty risk using NASA DAS was found to be 0.
Sapling is larger than 10 cm in its smallest dimension, and thus is presumed trackable. Sapling is registered with the 18th Space Defense Squadron. Through the 18th SPCS, Sapling can be tracked on spacetrack.com. Sapling’s nominal orbit transits the orbits of both the ISS and the Tiangong space stations, as well as planned flights of the SpaceX Dragon capsule. Upon receipt of a conjunction assessment, Stanford SSI operators will contact all other spacecraft operators involved in the probable collision and share Sapling Giganteum ephemeris and operational data, and work to develop a mitigation plan.
Orbital Debris Assessment Requirements
|Requirement (NASA Code)
|Description (As appears in NASA-STD-8719.14)
|All debris released during the deployment, operation, and disposal phases shall be limited to a maximum orbital lifetime of 25 years from date of release.
|The total object-time product shall be no larger than 100 object years per mission. For the purpose of this standard, satellites smaller than a 1U standard CubeSat are treated as mission-related debris and thus are bound by this definition to collectively follow the same 100 object-years per mission deployment limit.
|Limiting the risk to other space systems from accidental explosions during deployment and mission operations while in orbit about Earth or the Moon: For each spacecraft and launch vehicle orbital stage employed for a mission (i.e., every individual free-flying structural object), the program or project shall demonstrate, via failure mode and effects analyses, probabilistic risk assessments, or other appropriate analyses, that the integrated probability of explosion for all credible failure modes of each spacecraft and launch vehicle does not exceed 0.001 (excluding small particle impacts.).
|Limiting debris generated by collisions with large objects when in Earth orbit: For each spacecraft and launch vehicle orbital stage in or passing through LEO, the program or project shall demonstrate that, during the orbital lifetime of each spacecraft and orbital stage, the probability of accidental collision with space objects larger than 10 cm in diameter does not exceed 0.001. For spacecraft and orbital stages passing through the protected region +/- 200 km and +/-15 degrees of geostationary orbit, the probability of accidental collision with space objects larger than 10 cm in diameter shall not exceed 0.001 when integrated over 100 years from time of launch.
|Limiting debris generated by collisions with small objects when operating in Earth orbit: For each spacecraft, the program or project shall demonstrate that, during the mission of the spacecraft, the probability of accidental collision with orbital debris and meteoroids sufficient to prevent compliance with the applicable post mission disposal maneuver requirements does not exceed 0.01.
|Disposal for space structures in or passing through LEO: A spacecraft or orbital stage with a perigee altitude below 2,000 km shall be disposed of by one of the following three methods:
|a. Atmospheric reentry option:
|(1) Leave the space structure in an orbit in which natural forces will lead to atmospheric reentry within 25 years after the completion of mission or
|(2) Maneuver the space structure into a controlled deorbit trajectory as soon as is practical after completion of mission.
|b. Storage orbit option: Maneuver the space structure into an orbit with perigee altitude above 2000 km and ensure its apogee altitude will be below 19,700 km, both for a minimum of 100 years.
|c. Direct retrieval: Retrieve the space structure and remove it from orbit within 10 years after completion of mission.
|Limit the risk of human casualty:
|The potential for human casualty is assumed for any object with an impacting kinetic energy in excess of 15 joules:
|a. For uncontrolled reentry, the risk of human casualty from surviving debris shall be less than 0.0001 (1:10,000).
|b. For controlled reentry, the selected trajectory shall ensure that no surviving debris impact with a kinetic energy greater than 15 joules is closer than 370 km from foreign NASA-STD-8719.14C 50 of 77 landmasses, or is within 50 km from the continental U.S., territories of the U.S., and the permanent ice pack of Antarctica.
|c. For controlled reentry, the product of the probability of failure to execute the reentry burn and the risk of human casualty assuming uncontrolled reentry shall be less than 0.0001 (1:10,000).
|d. For long-term reentry of space structures in MEO, Tundra orbits, highly inclined GEO, and other orbits: Surviving debris shall have less than 7 m2 total debris casualty area or 0.0001 (1 in 10,000) risk of human casualty.