Reinventing Space Conference BIS-RS-2015-60 Small satellite launch vehicle from a balloon platform Kieran Hayward Cranfield University José Mariano López-Urdiales Founder, zero2infinity 13th Reinventing Space Conference 9-12 November 2015 Oxford, UK Small Satellite Launch Vehicle from a Balloon Platform Kieran Hayward1 and Jose Mariano Lopez Urdiales2 1 Cranfield University, Cranfield, UK 2 zero2infinity, Barcelona, Spain Abstract In the last decade there has been growing use of smaller satellites (0-100kg) to conduct Earth observation and science missions and this industry is growing. 2014 saw a small satellite launch increase of 72% compared with 2013. Companies such as Planet Labs are starting to launch large numbers of small satellites. However, to date the use of small satellites has been restricted due to the limited launch availability to this class of satellite. Due to their small size these satellites are normally launched as secondary payloads on larger launch vehicles (such as Falcon 9 or Ariane 5). This restriction has severely limited the launch dates available to these small satellites and also limits their orbit selection. Due to the restrictions mentioned above and building on its experience in high-altitude ballooning zero2infinity has begun designing a new small satellite launch vehicle, called bloostar. This three-stage vehicle is designed to put a 75kg payload into a 600km sun synchronous orbit. It is launched from a high altitude helium balloon at 20km, at this altitude the atmospheric density is low enough (<7% of sea level density) that aerodynamic drag is negligible. Traditional launch vehicles, which are launched from sea level have to pass through the densest part of the atmosphere, incurring large amounts of aerodynamic drag. By launching above the denser part of the atmosphere bloostar avoids these drag losses resulting in a significant Δ� saving. This reduction in atmospheric drag removes the need for an aerodynamic fairing around the payload, as the payload no longer needs to fit into an aerodynamic fairing, the constraints regarding payload volume are much reduced compared to existing launch vehicles. Additionally, the acoustic and shock environments are more benign which reduces the minimum thicknesses of components and overall satellite structural weight. This will allow light-weight, high volume satellites, such as small Earth observation telescopes which need larger diameter mirrors, to be launched. Launching at an altitude where aerodynamic drag is negligible also leads to a launch vehicle that is no longer required to be slender but instead is a series of concentric tori. This novel shape has a number of advantages, including allowing all engines to fire at the same time reducing inert mass of the first and second stages. The control system has to be adapted to the new geometry and mass distribution of the rocket. How much thrust vectoring and how much differential throttling of 13 engines is needed to optimize the trajectory even in engine out situations is the focus of some ongoing research. K. Hayward & J.M. Lopez-Urdiales BIS-RS-2015-60 Introduction Nano- (1-10kg) and micro-satellites (10-100kg) have proven their capabilities to perform increasingly complex missions effectively, affordably and responsively. Multiple factors have contributed to enhance their performance such as miniaturization of electronics and enhanced precision in small mechanical systems. There is an increasing interest in missions performed by nano/microsatellites with a whole new industry value chain emerging around them. For example, 2014 saw a small satellite launch increase of 72% compared with 2013 (Crisp, Smith, & Hollingsworth, 2014). Companies such as Planet Labs (Marshall & Boshuizen, 2013) are starting to launch large numbers of small satellites. The use of these smaller satellites has been restricted by the limited launch availability for this class of satellite. To date these satellites have been required to be launched as secondary (or tertiary) payloads on large launch vehicles such as Europe's Ariane 5 or SpaceX’s Falcon 9. Despite many competing efforts to develop has a launch vehicle solely for the purpose of launching small satellites (Niederstrasser, Frick, 2015) none has yet been fully developed. Those launchers which were being developed (for example Falcon 1) have been canceled as they were viewed by their manufacturers as non-profitable (or less profitable than launching larger satellite payloads). Being restricted to secondary payload spaces has severely limited the launch opportunities available to small satellites and also limits the selection of orbit location and launch date to existing planned launches. After identifying (Palerm, Barrera, Salas, 2013) that the true revolution in space capabilities would come not just from microsatellites but from the combination of microlaunchers and microsatellites (via responsive access and constellations) zero2infinity, a small Barcelona based start-up company, has begun development of a new launch vehicle specifically this market, bloostar. It is a three stage launch vehicle designed to put a 75kg payload into a 600km sun-synchronous orbit. It will be dropped from a helium balloon at an altitude of 20km. At this altitude the atmospheric density is low enough (<7% of sea level density) that aerodynamic drag can be neglected. This reduction in aerodynamic drag results in a significant Δ� saving (Beerer, 2014) and also means that instead of the long slender shape of ground launched vehicles bloostar is a series of concentric tori. This shape has a number of advantages over a slender body: this shape is easier to hoist by balloon; and it allows all rocket engines on every stage to be ignited in parallel reducing inert mass in the lower stages of the vehicle. 3 K. Hayward & J.M. Lopez-Urdiales BIS-RS-2015-60 Figure 1: bloostar rocket stack Advantages of Stratospheric Launch As mentioned in the introduction bloostar will be launched from a balloon at an altitude of 20km. Based on Astos simulations, it is expected that the launch vehicle will need approximately 9.28km/s of Δ� to reach a 600km polar orbit, compared to a Δ� of 10.12km/s for a ground launch (calculated from Astos simulations and Vega launcher data). While this may seem only a small difference (8%) using the Tsiolkowsky equation it can be shown by assuming a specific impulse of 3,250m/s (typical of a methane fueled rocket) that the initial mass of bloostar at launch would be approximately 30% larger than if launched at altitude. The benefits of launching at altitude are further shown by considering the graph in Figure 2 which shows that by launching at 20km drag losses can be as much as 22.5 times less. In addition to the reduced Δ� and atmospheric drag launching at altitude also results in reduced payload vibration, which reduce the impact of launch to sensitive scientific instruments, and also reduced height transfer, shown in Figure 3. 4 K. Hayward & J.M. Lopez-Urdiales BIS-RS-2015-60 Figure 2: Drag vs. altitude for a generic launcher ignited from ground (red) and 20km (blue) Figure 3: Heat flux vs. time for generic launcher ignited from ground (red) and 20km (blue) The only existing air launched orbital rocket, Orbital’s Pegasus experiences a maximum dynamic pressure (maxq) of 67kPa. With bloostar the maxq is only 5kPa. This has implications on the structural weight of the launcher. 5 K. Hayward & J.M. Lopez-Urdiales BIS-RS-2015-60 Compared to aircraft assisted launchers, there is no need for wings, fins, or heavy control system actuators, auxiliary power units, etc. The trajectory, higher control authority, and the structural shape of the rocket remove the typical longitudinal bending of air launch pull up maneuvers. This forced X-15, SpaceShipOne and Pegasus to have a heavier and reinforced fuselage, never carrying over 63% of their own gross weight as propellant. All of the benefits discussed above result in a launch vehicle which is significantly simpler and cheaper to operate which results in a reduced launch cost for the small satellite community. Configuration The following is a mass budget of the bloostar rocket stack. 1st stage 2nd stage 3rd stage Structural mass (kg) 552.7 118.8 103.7 Fairing (kg) 25 0 0 Propellant mass (kg) 3284.6 622.6 218.7 Total stage mass (kg) 3862.3 741.4 322.4 Stage “Payload” (kg) 1138.8 397.4 75 Engine Isp (s) 342 342 342 Ideal deltaV (m/s) 3587.8 2654.6 2681.4 deltaV share (%) 40.2 29.8 30 Figure 4: bloostar exploded view Concept of operation bloostar will be launched from a ship reducing the risk of launch delays. Several launch windows can be mapped over the surface of the ocean and the one with least chances of weather delays can be selected. Additionally, the ship can move at the speed of the wind and thus compensate ground winds. A near zero wind column is generated in which to inflate and release the balloon 6 K. Hayward & J.M. Lopez-Urdiales BIS-RS-2015-60 from the deck. The ship itself does not need any significant adaptation for the operation. Any ship with a sufficiently big flat area to fit the ISO containers where all the system can be packed could be rented to perform the flight. The payload is mounted near the balloon inflation area. The effective launch area should be of around 50x17 meters. The chosen location for the initial launches is the south west of the Canary Islands due to the calm seas and low wind speeds generated by the constant weather patterns and the geographic characteristics of the islands. This location is also excellent to choose a desired orbit since most azimuths are available. The first phase of the flight is a balloon ascent to Near Space (20 km) during approximately 90 minutes.