Spaceflight from Super-Earths is difficult

Hippke, Michael

doi:10.1017/s1473550418000198

Cited by 4 publications

(2 citation statements)

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“…for a given stellar mass (M ) and semi-major axis of the planet (a). We have not considered the conditions for escaping the planet's gravity, which has been investigated in Hippke (2018). It can, however, be verified that the corresponding velocity for escaping the planetary surface is likely to be lower than v esc for M M if we consider rocky planets in the habitable zones of their host stars.…”

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Limitations of Chemical Propulsion for Interstellar Escape from Habitable Zones Around Low-mass Stars

Lingam

Loeb

2018

Res. Notes AAS

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On Earth, current and past space missions have been reliant on chemical rockets (Crawford 1990). A notable issue with chemical rockets is that the mass of the fuel required (for a given payload) scales exponentially with the final speed that one wishes to achieve. Fortunately, this issue is not particularly important for humanity because the escape velocities from the Earth and the Solar system are roughly within an order of magnitude of the velocities achievable by chemical rockets. However, the use of chemical rockets for undertaking interstellar travel is likely to become more problematic for habitable planets around low-mass stars, for reasons outlined below. In this work, we carry out calculations to quantify, and further develop, the general points raised in Loeb (2018).The rocket equation developed by Tsiolkovsky (1903) states thatwhere m 0 and m f are the initial (payload and fuel) and final (only payload) masses respectively, v ex is the exhaust velocity and ∆v is the maximum velocity change that can be achieved. For state-of-the-art rockets that use liquid oxygen-hydrogen fuel, v ex = g ⊕ I sp where g ⊕ = 9.8 m/s 2 is the Earth's surface gravity and I sp ∼ 450 s is the specific impulse. If we wish to exit the planetary system, ∆v v esc is necessary, with the escape speed v esc defined asfor a given stellar mass (M ) and semi-major axis of the planet (a). We have not considered the conditions for escaping the planet's gravity, which has been investigated in Hippke (2018). It can, however, be verified that the corresponding velocity for escaping the planetary surface is likely to be lower than v esc for M M if we consider rocky planets in the habitable zones of their host stars. In our discussion below, we will adopt the criterion ∆v > (1 − 1/ √ 2)v esc instead, where the additional factor has been introduced to account for the boost from gravitational assists. This reduction in ∆v is achievable by launching the rocket such that it will be parallel to the planet's motion (Loeb 2018). In this scenario, the planet's speed in a circular orbit is v c = GM /a and therefore ∆v = v esc − v c is given by ∆vAlthough v esc depends on two independent parameters, we can reduce this to just one parameter by demanding that the technological species inhabit an "Earth-analog", i.e. a habitable planet that receives the same insolation as the Earth so as to possess surface liquid water, which is necessary for the chemistry of "life as we know it". In this event, we have a ∝ L 1/2 with L denoting the stellar luminosity. Thus, using the above data in (1), we find that the lower bound on m 0 /m f is given byand we can make use of the mass-luminosity relation from Loeb et al. (2016) to express the right-hand-side purely as a function of M . The final result has been plotted in Fig. 1, and it is evident that m 0 /m f becomes very high for

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Limitations of Chemical Propulsion for Interstellar Escape from Habitable Zones Around Low-mass Stars

Lingam

Loeb

2018

Res. Notes AAS

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“…The search for alternative fuel sources, especially for interstellar travel, has been the subject of much recent exploration. Recent work has also explored the difficulty of exoplanetary civilizations using chemical rockets to escape super-Earths (Hippke 2018;Loeb 2018). Electric sails and magnetic sails have been among the proposed alternatives that do not require any onboard fuel (Lingam & Loeb 2020).…”

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Reflection from Inclined, Relativistic Light Sails

Bari

2023

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A Review on Substellar Objects below the Deuterium Burning Mass Limit: Planets, Brown Dwarfs or What?

Caballero

2018

Geosciences

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Free-floating, non-deuterium-burning, substellar objects" are isolated bodies of a few Jupiter masses found in very young open clusters and associations, nearby young moving groups and in the immediate vicinity of the Sun. They are neither brown dwarfs nor planets. I look over their nomenclature, history of discovery, sites of detection, formation mechanisms and future directions of research. Most free-floating, non-deuterium-burning, substellar objects share the same formation mechanism as low-mass stars and brown dwarfs, but there are still a few caveats, such as the value of the opacity mass limit, the minimum mass at which an isolated body can form via turbulent fragmentation from a cloud. The least massive free-floating substellar objects found to date have masses of about 0.004 Msol, but current and future surveys should aim at breaking this record. For that, we may need LSST, Euclid and WFIRST.

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Spaceflight from Super-Earths is difficult

Cited by 4 publications

References 24 publications

Limitations of Chemical Propulsion for Interstellar Escape from Habitable Zones Around Low-mass Stars

Limitations of Chemical Propulsion for Interstellar Escape from Habitable Zones Around Low-mass Stars

Reflection from Inclined, Relativistic Light Sails

A Review on Substellar Objects below the Deuterium Burning Mass Limit: Planets, Brown Dwarfs or What?

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