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AFS 6 Orbit Design Process: 5 AFS 6 Orbit design process: 5. Mission Orbit Design Trades - A New element: Re-usability of launcher - Space-X, a US company started and owned by Elon Musk has a rocket called Falcon-9. It currently cost 54M$ - It has succeeded with a number of launches but the idea is to recover the first stage Exercise: Find informaon on the net and do: 1. Find the es4mates for the resusability, i.e. How many 4mes can a 1:st stage be launched? How many launches will an engine survive? What are the poten4al savings when regular landings of stage 1 is acheived? 2. Write a short text where you discuss the poten4al impact on scien4fic missions. Will there be more? Will the cost savings on the launcher impact the cost of the payload? Keplerian orbit transfers Single impulsive manoeuvre: Initial and final orbit intersect at the point of impulse. Single manoeuvres can only transfer s/c between intersecting orbits! Simplest case is for a co-planar transfer from circular orbit to elliptic orbit. If velocity is increased è semi- major axis will be expanded At least two manoeuvres are required to transfer s/c between non-intersecting orbits Hohmann transfer orbit è two coplanar manoevres to go from one small circular orbit to a large one Simple calculation accordingly 1 2 µ µ V − = ε ε = − 2 r 2a € € Planet a(AU)transfer T(years) ΔV (km/s) Mercury 0.847 0.289 5.6 Venus 0.931 0.400 3.5 Mars 1.131 0.709 3.6 Jupiter 2.051 2.731 6.3 Saturn 3.137 6.056 7.3 Uranus 5.534 15.972 8.0 Neptune 8.253 30.529 8.3 Pluto 10.572 45.208 8.4 Help is on the way: Gravity assist Specific Impulse, Isp is the total impulse per unit propellant weight consumed Tsiolkovsky equation in field- ΔV = Ve lnR free space (1903) M Initial to burnout mass R = 0 Mb € € Rocket equation: - Basic parameters: Thrust & Specific Impulse A = nozzle exit area Thrust è e F = m˙ V e + Ae[Pe − P∞] ≈ m˙ Ve Pe = gas pressure at nozzle exit P∞ = Ambient pressure Ve = propellant exhaust velocity and m ˙ = propellant mass flow Ae C = effective exhaust velocity C ≡ Ve + [Pe − P∞ ] € m˙ € F è F = m˙ C The Specific Isp = Inpulse, Isp m˙ g - Ispis a measure of energy€ content of propellant/how efficiently it is converted to thrust, F - For chemical rocket , I is proportional to square sp T root of ratio of chamber temperature, Tc to average c Isp = K € molecular weight of exhaust gases, Mgas . € Mgas € Rocket equaon: Primary measure of propulsion system performance is the velocity change, ΔV, that can be produced. This parameter is given by the rocket equation: $ ' $ ' m0 m0 ΔV = gIsp ln& ) ≡ gIsp ln& ) ≡ gIspR % m0 − mp ( % m f ( where m f ≡ m0 − mp Are the final vehicle mass and mass ratio respectively m € R ≡ 0 m f m0 is initial mass and mp is propellent mass respectively. This equation assumes zero drag and gravity losses and is a limiting ideal case. € Typical loss and gravity losses (close to the Earth) are 1500 to 2000 m/s Rocket equaon: Another form of the rocket equation expresses the mass of propellant for a given increment of velocity ΔV: m m e(ΔV / I sp g) 1 m 1 e−(ΔV / I sp g) p = f [ − ] = 0[ − ] - Highest thrust is when exit pressure = ambient pressure - When exit pressure is higher than ambient pressure, exhaust velocity goes down € - Rocket nozzles are designed to take this into account when possible. The exit pressure is governed by the nozzle-area expansion ratio: A ε = e At Where Ae is exit area and At is nozzle throat area € Jet engine 6000s 300 m/s Solid rocket 250s 2500 m/s Liquid rocket 542s 5320 m/s Ion engine 3000s 29000 m/s Nuclear rocket 1000s 8340 m/s VASIMIR 30000s 210000 m/s Variable specific impulse magnetoplasma rocket (VASIMIR) propulsion Purely hypothetical at moment Exercise: Search on the web for more information on current propulsion systems. What is a VASIMIR propulsion system. Write a short report and try to draw conclusions about the possibilities to explore the Solar System in the future: Will we ever have cheap and fast space travel? Orbits: LEO: Low Earth Orbit, altitude < 2000 km Space Shuttle, ISS, HST, Iridium, Remote sensing (Landsat, Envisat), military (communication, intelligence) MEO: Medium Earth Orbit, altitude < 20000 km GPS: NAVSTAR, Galileo GEO: Geosynchronous Earth Orbit, altitude = 36000 km Meteorology, Communication (Signal relays for terrestrial broadcast and cable systems; Direct broadcast satellite radio & TV), TDRS (Tracking and Data Relay Satellite) Astronomy missions: Requirements (examples) Cooling Go as far away from the Earth/Moon as possible – put shield between s/c and Sun Particles Either below or above radiation belts L2, drift away orbits are new and little information exist High Far away from the Earth, L2 is maybe cadence not ideal for all sky coverage (no or little interruptio ns) International Ultraviolet Explorer TELESCOPE : 45 cm, f/15 Ritchey-Chretien Cassegrain SPECTROGRAPHS : Echelle (1150 Å to 1980 Å and 1800 Å to 3350 Å) Dimensions: 142 × 422 cm Launch vehicle/site: Delta 2914, from Cape Canaveral, Florida Launch mass: 671 kg (122 kg science, 237 kg apogee boost motor) Orbit: Geo-synchronous over Atlan4c: ini4ally 32 050×52 254 km, 28.6º, 23.927 h; at mission end 36 360×48 003 km ,35.9º Lanched: January 26 1978 Deliberately turned off: 30 September 1996 (Designed for 2 ½ years) XMM-Newton 4 tonnes, 10m long launched on Ariane 504 in 1999 Produces one scientific publication per orbit Highly elliptical orbit, with an apogee of about 114,000 km and a perigee of ca. 7000 km (the minimum elevation for science observations will be 40,000 km); Orbital elements allow maximum visibility of s/c from southern hemisphere Herschel & Planck Lagrangian points in 2-body system ISO: Infrared Space Observatory November 1995 – April 1998 Highly Elliptical Geocentric Orbit (HEO) Apogee 70600 km Perigee 1000 km T 24h Decaying orbit Infrared Astronomy -- Definitions IR divided roughly in three separate regions (note: different from other disciplines): Thermal region NIR – 0.8 µm – 5 µm è ~ thousands K – 740K MIR – 5 µm – (25-40) µm è 740K – (140-90)K FIR (25-40) µm – (200-350) µm è (140-90)K – (20-10)K Pushing into the far infrared and submillimetre • Longer wavelengths means colder temperatures Infrared Astronomy -- Definitions In IR and sub-mm (radio) we use the Jansky as the unit for flux density The flux density or monochromatic flux, S, of a source is the integral of the power beamed into a solid angle Ω, Β The Jansky or Jy is defined as 10-26 W m-2 Hz-1 FIR (25-40) µm – (200-350) µm è (140-90)K – (20-10)K Sources of Infrared radiation 1. Radiation from dust 4. Line emission from nebulae - Cool dust 10 – 50 K - H-recombination lines (Brackett, - Molecular clouds Pfund, etc) - Outer parts of starforming disks - Forbidden lines from ions (OIII, - Debris disks SIV, NeII) - Kuiper-Edgeworth belts - Warm dust 50K – 300K 5. Line emission from molecular clouds - Inner parts of starforming disks (Vibro transitions in IR, rotational - Zodiacal dust transitions in sub-mm and mm) - Hot dust 300K -- ~ 1200K - Inner part of starforming disks 6. Late type stars (NML Cyg, NML Tau), - Centre of galaxies Early stars (Shell stars) 2. Thermal plasma - free-free emission 3. Non-thermal plasma - synchroton emission Astronomy from Space Lesson 7 .
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