VLEO satellites — A new earth observation space systems commercial and business model

摘要

Low earth orbits are defined as orbits with altitude below 2000km, these orbits provide superior advantages for earth observations missions. The distinction between VLEO and LEO is the altitude of the former is below 500km. VLEO missions possess great advantages such as, in maritime surveillance, illegal immigration and piracy this is due to the fact that the imagery capabilities are enhanced significantly and identification of small objects in the order of 1 meter is feasible, in addition to higher frequency of intraday location inspection visits. These are some of the great benefits for home land security and national security of any country. In order for satellites to operate at such low altitude orbit for a long, sustained period of time, new technologies should be developed and radical satellite design change departing from current LE orbit state of the art technologies should be implemented. Since, the satellites will be operating in rarified aerodynamics environments. In this environment the satellite can operate for long sustained period of time utilizing air breathing electric propulsion to compensate for the drag, this has the advantage of not carrying propellant payload, and also can be utilized for deorbiting the satellite reducing space debris. Therefore, the operation life of the satellite is decoupled from propellant mass payload restriction, and is limited by other spacecraft subsystems. Technologies associated with new combination of new aerodynamic materials and aerodynamic controls are also required to commercialize VLEO Spacecraft platforms. These technologies are essential for developing commercial and economic models for Low earth observations space platforms. In order for the commercial and economic model be sustainable, the paper will focus on review of the emerging VLEO technologies that can be utilized to make the commercial and economic model viable. VLEO can improve payloads performance, for the same aperture size the optical resolution can be enhanced due to decrease in distance. Or the same resolution can be maintained with lower mass payloads and size. Further benefits can be gained for example for radar payloads as reduced altitude can decrease transmitted power requirements and reduce the area of the antenna. Furthermore, for radar and communication detectors the radiometric performance will improve as well due to dependency on the inverse square law. Despite the drag penalty, this can be utilized for attitude and orbit control capabilities. Due to the rarefied aerodynamic environment the lift forces are small compared to the drag forces, however certain spacecraft's design can capitalize on this fact not only to stabilize the space craft but also direct it to towards the airflow direction which is desirable from the standpoint of view of air breathing electric propulsion system. Incorporating controllable surfaces in the design can create aerodynamic torques delivering attitude and point control capability. This in turn can reduce the mass as other control attitude subsystem will not be required. VLEO also impacts mission and system design due to reduced payloads with higher resolution capability, the cost and size of the spacecraft will also be reduced and the outcome is more number of launches with lower cost per launch which will make the business model more affordable for smaller companies. In addition de-orbiting at end-of life is achieved as VLOE debris has a faster decay rate and therefore orbits are more resilience for debris accumulation. The outcome of this more affordability is to create constellation of spacecraft network and therefore better coverage. The gas surface interaction dominates the rarified aerodynamic flow regimes with molecular mean free path exceeding the satellite typical length. Meaning atomic oxygen from the atmosphere are adsorbing or eroding the material. This process is influenced on variety of parameters such as, incident gas composition velocity and angel, surface temperatures, surface cleanliness and roughness and surface molecular composition and lattice configuration. Atmospheric breathing electric propulsion has a great promise; atmospheric residual oxygen at low earth orbit is collected and used as a propellant for electric thruster. This has an advantage compared with other propulsion technologies such as GIT (gridded ion thruster) or hall effect thrusters (HET) which can experience lower performance over time due erosion of the accelerated grids or the discharge panels. Great efforts are currently being invested towards the investigation of inductive plasma thrusters (IPT). IPT's has several advantages, the flexibility of the propellant which is dependent on the atmospheric altitude, no erosion since it is electrodeless and griddles and neutraliser is not required. The main challenges associated with VLEO spacecraft's with emphasis on Atmospheric Breathing Electric propulsion, orbital aerodynamics and satellite drag, and material and processes to reduce induced drag will be discussed and reviewed for VLEO satellites to establish a new disruptive commercial and business model dedicated for low earth observation space systems. This model will enhance the number of payloads launches and reduce launch costs, therefore opening the way for small companies to enter this segment with new innovative payloads and spacecraft design to promote security and the wellbeing.