The balloon gondola will be housing the telescope or scientific payload and all required support systems for the payload. Balloon gondolas are normally developed for a specific mission and payloads are usually flown a couple of times at the most, depending on the scientific goals program. However, the ESBO gondola will be designed to be re-flown many times. The support systems will be developed with high modularity, scalability, flexibility and reusability as a baseline. This will enable easy adaption of the gondola to different telescopes and missions. The reusability aspect will make it possible to fly the instrument frequently and maximize the flight and observation time with the different telescopes and at the same time reduce cost and time for refurbishment of gondola and support systems in between flights. Some aspects that are important for the gondola design are:
- Mechanical stiffness;
- Thermal protection for instruments;
- Easy integration and disintegration;
The gondola will be equipped with support systems for the different telescopes/instruments to be flown such as:
- Mechanical gondola structure;
- Power system;
- Communication system;
- Thermal control system;
- Gondola control and coordination system;
- Landing and recovery system.
The subsystems will be reused from mission to mission in order to reduce cost and development time for the program. The focus can then be on the development of instruments, telescopes, and flight or observation time.
At termination of the flight, the gondola is separated from the balloon and traditionally descends on a non-steerable parachute down to the ground following the wind. Owing to the flight trajectories and the maximum use of observation time, the landing and recovery of the gondola in most cases take place in remote areas. Depending on the terrain and wind conditions, the landing can be rough, causing damage to both the gondola and instrument. To mitigate this and reduce the risk of damages, especially important in the ESBO case where the gondola and instrument are foreseen to re-fly often, novel landing systems will be foreseen such as steerable parafoils and potentially air bags. The use of steerable parafoils will not only allow the reduction of structural landing loads, but also a choice of the landing zone within the operating radius of the parafoil system, promising a significant reduction of recovery efforts.
Attitude control system
The telescope has to be pointed towards the desired object on the sky for observation in azimuth and elevation. This will be achieved by a two-stage system. The first stage will be performed by a coarse control system, turning the complete gondola 360° for azimuth and tipping the telescope around its mounting axis for elevation pointing. The coarse system will function largely independently from the inner stage, employing its own attitude sensors, including differential GPS, gyroscopes, and a star tracker. There will be a limitation around zenith elevation due to the balloon obscuring the field of view. The limitations are dependent on the size of the balloon and the distance between the balloon and the gondola. The coarse pointing system to be developed and used for ESBO will be based on previous designs used on the astronomic PoGO balloon missions.