Editing Spacecraft propulsion (section)

===Advanced propulsion technology===
Advanced, and in some cases theoretical, propulsion technologies may use chemical or nonchemical physics to produce thrust but are generally considered to be of lower technical maturity with challenges that have not been overcome.{{Sfn|Meyer|2012|p=20}} For both human and robotic exploration, traversing the solar system is a struggle against time and distance. The most distant planets are 4.5–6 billion kilometers from the Sun and to reach them in any reasonable time requires much more capable propulsion systems than conventional chemical rockets. Rapid inner solar system missions with flexible launch dates are difficult, requiring propulsion systems that are beyond today's current state of the art. The logistics, and therefore the total system mass required to support sustained human exploration beyond Earth to destinations such as the Moon, Mars, or [[near-Earth object]]s, are daunting unless more efficient in-space propulsion technologies are developed and fielded.{{Sfn|Meyer|2012|p=6}}<ref name=huntsb>
{{cite journal
|doi=10.1061/40476(299)45
|citeseerx = 10.1.1.83.3242
|title=Robotics Challenges for Robotic and Human Mars Exploration
|journal=Robotics 2000
|year=2000
|last1=Huntsberger
|first1=Terry
|last2=Rodriguez
|first2=Guillermo
|last3=Schenker
|first3=Paul S.
|isbn=978-0-7844-0476-8
|pages=340–346}}</ref>

A variety of hypothetical propulsion techniques have been considered that require a deeper understanding of the properties of space, particularly [[Inertial frame of reference|inertial frames]] and the [[vacuum state]]. Such methods are highly speculative and include:{{citation needed|date = July 2023}}{{colbegin}}
*[[Black hole starship]]
*[[Breakthrough Propulsion Physics Program#Quantum vacuum energy experiments|Differential sail]]
*[[Gravitational shielding]]
*[[Field propulsion]]
**Diametric drive
**Disjunction drive
**Pitch drive
**Bias drive
*[[Photon rocket]]
*[[Quantum vacuum thruster]]
*[[Nano electrokinetic thruster]]
*[[Reactionless drive]]
**[[Abraham–Minkowski controversy|Abraham—Minkowski drive]]
**[[Alcubierre drive]]
**[[Dean drive]]
**[[EmDrive]]
**[[Heim theory]]
**[[Woodward effect]]

{{colend}}

A NASA assessment of its [[Breakthrough Propulsion Physics Program]] divides such proposals into those that are non-viable for propulsion purposes, those that are of uncertain potential, and those that are not impossible according to current theories.<ref>{{cite conference
 | first =Marc
 | last =Millis
 | title =Assessing Potential Propulsion Breakthroughs
 | book-title =New Trends in Astrodynamics and Applications II
 | date =June 3–5, 2005
 | location =Princeton, NJ
 | url =https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20060000022.pdf
 }}</ref>