A Discrete, Energetic Approach to Rocket Propulsion

Autor/in	Blanco, Philip R.
Titel	A Discrete, Energetic Approach to Rocket Propulsion
Quelle	In: Physics Education, 54 (2019) 6, Artikel 065001 (6 Seiten)Infoseite zur Zeitschrift PDF als Volltext Verfügbarkeit
Zusatzinformation	ORCID (Blanco, Philip R.)
Sprache	englisch
Dokumenttyp	gedruckt; online; Zeitschriftenaufsatz
ISSN	0031-9120
Schlagwörter	Physics; Motion; Scientific Concepts; Fuel Consumption; Kinetics; Energy; Introductory Courses; Undergraduate Students; College Science; Engineering + Suchen Sie Ihr Suchwort? Physik; Bewegungsablauf; Benzinverbrauch; Kinetik; Energie; Einführungskurs; Maschinenbau
Abstract	Most rockets convert the energy stored in their propellant mass into the mechanical energy required to expel it as exhaust. The 'rocket equation', which describes how a rocket's speed changes with mass, is usually derived by assuming that this fuel is expelled at a constant relative velocity. However, this is a poor assumption for cases where the rocket promptly loses a large fraction of its mass. Instead, I derive the change in speed for a rocket that emits its fuel in N discrete pellets, with a constant mechanical energy produced per unit fuel mass. In this model I find that the rocket's speed change is greatest when all the fuel is expelled at once (N = 1). In the limit of many small pellets (N ? [infinity]), I show that the velocity change approaches, from above, the prediction of the continuous thrust rocket equation. For this model of rocket propulsion, I quantify how the fuel's total available energy is divided between the rocket and exhaust. In the limit of continuous thrust, the rocket can utilise no more than 65% of the available mechanical energy as its kinetic energy. In an online supplement, I compare this model of discrete propulsion with those previously published. This topic uses momentum conservation and mechanical energy concepts at the introductory undergraduate level. (As Provided).
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Erfasst von	ERIC (Education Resources Information Center), Washington, DC
Update	2020/1/01