Advanced Pulsed Plasma Thruster Demonstration On MightySat Flight II.1

This paper describes the progress associated with a joint effort to demonstrate an advanced pulsed plasma thruster (PPT) on MightySat Flight II.1 to be launched in January, 1999. The PPT currently being developed for this flight represents a significant leap in technology compared to previous flight models. Although the MightySat II.1 launch vehicle is yet to be determined, the Space Shuttle Hitchhiker Eject System is the primary option under consideration. With this launch option, the PPT will be used to extend MightySat 11.1 life from about 1-3 months to over one year by raising its operational orbit. The PPT is an ideal propulsion system for extending small satellite life because of its high specific impulse (\u3e 1000 sec), low system wet mass \u3c 5 kg), and inert nature when unpowered (thus minimizing Shuttle integration issues). In addition to the life enhancement mission, the on-orbit operations have been specifically designed to rigorously test the PPT and to demonstrate its compatibility with the MightySat II.1 spacecraft in order to validate it for future DoD, NASA, and commercial satellites

Measurements of the neutron spectrum in transit to Mars on the Mars Science Laboratory

The Mars Science Laboratory spacecraft, containing the Curiosity rover, was launched to Mars on 26 November 2011. Although designed for measuring the radiation on the surface of Mars, the Radiation Assessment Detector (RAD) measured the radiation environment inside the spacecraft during most of the 253-day, 560-million-kilometer cruise to Mars. An important factor for determining the biological impact of the radiation environment inside the spacecraft is the specific contribution of neutrons with their high biological effectiveness. We apply an inversion method (based on a maximum-likelihood estimation) to calculate the neutron and gamma spectra from the RAD neutral particle measurements. The measured neutron spectrum (12–436 MeV) translates into a radiation dose rate of 3.8±1.2 μGy/day3.8±1.2 μGy/day and a dose equivalent of 19±5 μSv/day19±5 μSv/day. Extrapolating the measured spectrum (0.1–1000 MeV), we find that the total neutron-induced dose rate is 6±2 μGy/day6±2 μGy/day and the dose equivalent rate is 30±10 μSv/day30±10 μSv/day. For a 360 day round-trip from Earth to Mars with comparable shielding, this translates into a neutron induced dose equivalent of about 11±411±4 mSv

The Radiation Assessment Detector (RAD) Investigation

The Radiation Assessment Detector (RAD) on the Mars Science Laboratory (MSL) is an energetic particle detector designed to measure a broad spectrum of energetic particle radiation. It will make the first-ever direct radiation measurements on the surface of Mars, detecting galactic cosmic rays, solar energetic particles, secondary neutrons, and other secondary particles created both in the atmosphere and in the Martian regolith. The radiation environment on Mars, both past and present, may have implications for habitability and the ability to sustain life. Radiation exposure is also a major concern for future human missions. The RAD instrument combines charged- and neutral-particle detection capability over a wide dynamic range in a compact, low-mass, low-power instrument. These capabilities are required in order to measure all the important components of the radiation environment. RAD consists of the RAD Sensor Head (RSH) and the RAD Electronics Box (REB) integrated together in a small, compact volume. The RSH contains a solid-state detector telescope with three silicon PIN diodes for charged particle detection, a thallium doped Cesium Iodide scintillator, plastic scintillators for neutron detection and anti-coincidence shielding, and the front-end electronics. The REB contains three circuit boards, one with a novel mixed-signal ASIC for processing analog signals and an associated control FPGA, another with a second FPGA to communicate with the rover and perform onboard analysis of science data, and a third board with power supplies and power cycling or "sleep"-control electronics. The latter enables autonomous operation, independent of commands from the rover. RAD is a highly capable and highly configurable instrument that paves the way for future compact energetic particle detectors in space

Mars' surface radiation environment measured with the Mars science laboratory's curiosity rover

The Radiation Assessment Detector (RAD) on the Mars Science Laboratory’s Curiosity rover began making detailed measurements of the cosmic ray and energetic particle radiation environment on the surface of Mars on 7 August 2012. We report and discuss measurements of the absorbed dose and dose equivalent from galactic cosmic rays and solar energetic particles on the martian surface for ~300 days of observations during the current solar maximum. These measurements provide insight into the radiation hazards associated with a human mission to the surface of Mars and provide an anchor point with which to model the subsurface radiation environment, with implications for microbial survival times of any possible extant or past life, as well as for the preservation of potential organic biosignatures of the ancient martian environment

Mars' surface radiation environment measured with the Mars science laboratory's curiosity rover

The Radiation Assessment Detector (RAD) on the Mars Science Laboratory’s Curiosity rover began making detailed measurements of the cosmic ray and energetic particle radiation environment on the surface of Mars on 7 August 2012. We report and discuss measurements of the absorbed dose and dose equivalent from galactic cosmic rays and solar energetic particles on the martian surface for ~300 days of observations during the current solar maximum. These measurements provide insight into the radiation hazards associated with a human mission to the surface of Mars and provide an anchor point with which to model the subsurface radiation environment, with implications for microbial survival times of any possible extant or past life, as well as for the preservation of potential organic biosignatures of the ancient martian environment

The Hohmann-Parker Effect Measured by the Mars Science Laboratory on the Transfer from Earth to Mars: Consequences and Opportunities

We show that a spacecraft launched from Earth towards Mars following a Hohmann minimum energy transfer trajectory has a strong tendency to remain well-connected magnetically to Earth, in the early phase of the transfer, or to Mars in the late phase, via the Parker spiral magnetic field. On the return trip, the spacecraft would remain reasonably well-connected magnetically first to Mars and later to Earth. Moreover, good magnetic connectivity occurs on all Hohmann transfers between neighboring planets in the inner solar system out to Mars. We call this hitherto unnamed circumstance the Hohmann-Parker effect. We show consequences of the effect by means of simultaneous cosmic radiation proxy observations made near Earth, near Mars, and at the Mars Science Laboratory on the transfer from Earth to Mars in 2011/2012. We support the observations with simulations of the large-scale magnetic field of the inner heliosphere during this period and compare the results with our predictions. The implications of the Hohmann-Parker effect are discussed