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Small Spacecraft Transfer Stage Development


Scope Title:

SmallSpacecraft Transfer StageDevelopment


NASA andindustry represent prospective customers for sending small spacecraftpayloads in the near term to the cislunar environment, with longer termpotential for farther destinations such as near-Earth objects, Mars, orVenus. The lunar destinations in this case include the lunar surface,with specific interest in the south pole, low lunar and frozen lunarorbits; and cislunar space, including Earth-Moon Lagrange points (e.g.,E-M L3) and the lunar near-rectilinear halo orbit (NRHO) intended forGateway. In future missions, NASA may transport small spacecraft toVenus for scientific discovery, to Mars to serve as precursors andinfrastructure for human (and scientific) exploration, and on smallspacecraft missions to near-Earth objects for science measurementsneeded to understand prospective threats to Earth and perhaps even forresource extraction and return to Earth. The ultimate goal is to exploitthe advantages of low-cost and rapidly produced CubeSats and smallspacecraft, defined as total mass less than 180 kg fueled, by enablingthem to reach these locations. Due to the current limits of SmallSatpropulsion capabilities and the constraints of rideshare opportunities,NASA has an interest in the development of a low-cost transfer stage toguide and propel small spacecraft on trajectories to the vicinity of theMoon and enable their insertion into the above-referenced orbits. Inaddition, NASA has interest in the transfer stage being able to providesupport services to the spacecraft post-deployment, such ascommunications relay or PNT services. Advancement and extension of thesecapabilities will be needed for future planetary exploration.

NASA seeks proposals for thedevelopment, improvement, or maturation of small spacecraft stagedesigns to increase performance, reliability, and/or safety. While theend goal of this topic is a stage-level design, an initial targetedfocus on propulsion system component or subsystem-level development isacceptable as long as there is detailed discussion and planning for itsintegration into a stage-level design. Transfer stage designs shall becompatible with U.S. small launch vehicles that are currently flying orwill be launching imminently. Proposals shall identify one or morerelevant small launch vehicles, describe how their designs fit withinthe constraints of those vehicles, and define the transfer capability ofthe proposed system (i.e., from low Earth orbit (LEO), geosynchronoustransfer orbit (GTO), etc., to low lunar orbit (LLO), NRHO, E-M L3,etc.).  Establishment of a partnership or cooperative agreementwith a launch vehicle provider is strongly encouraged. Transfer stagedesigns shall contain all requisite systems for navigation, propulsion,and communication in order to complete the mission. Novel propulsionchemistries and methods may be considered, including electricpropulsion, as long as the design closes within the reference missionconstraints. Transfer stages shall also include method(s) to deploy oneor more SmallSat payloads into the target trajectory or orbit.Innovations such as novel dual-mode propulsion systems that enable newscience missions or offer improvements to the efficiency, accuracy, andsafety of lunar missions are of interest. Concepts that enable smallcargo delivery and inspections to support on-orbit servicing, assembly,and manufacturing platforms are also desired. Additionally, technologieswith dual-use potential (such as hypersonic or suborbitaldemonstrations) are applicable to this subtopic. The ability of thetransfer stage to provide support services, such as communications relayor PNT, after spacecraft deployment is highlydesirable.   

This subtopic is targeting transferstages for launch vehicles that have a capability range similar to thatsought by the NASA Venture Class Launch Services. Rideshare applicationsthat involve medium- or heavy-lift launch vehicles (e.g., Falcon 9,Atlas V) or deployment via the International Space Station (ISS) airlockare not part of this topic.

Lunar design reference mission:

  • Launch on a small launch vehicle(ground or air launch).
  • Payload (deployable spacecraft)mass: at least 50 kg.
  • Provide sufficient delta-v andguidance to enter into translunar injection (TLI) orbit after separationfrom small launch vehicle. An example mission is the Cislunar AutonomousPositioning System Technology Operations and Navigation Experiment(CAPSTONE)/NRHO Pathfinder 12U (25 kg) CubeSat, which requires a TLIorbit with a C3 (characteristic energy) of -0.6km2/s2.
  • (Alternative) Provide sufficientdelta-v and guidance to place a >50-kg spacecraft directly intolunar NRHO or E-M L3 orbit.
  • Deploy spacecraft from transferstage.
  • Perform transfer stage safing anddisposal operations.

Stretch goals are:

  1. Extensibility of the design forplanetary design reference missions: Similar to the above, for Venus,Mars, or near-Earth object destinations.
  2. Ability to provide support services,such as communications relay and/or PNT, post spacecraft deployment.Proposer to outline the performance and duration these support servicescan achieve for applicable orbital environments, but it is envisagedthat at a minimum:
    • The transfer stage is compatiblewith the Deep Space Network (DSN), or equivalent asset, forcommunications and tracking, and its estimated position can bedetermined at values in line with the current state of the art for thetarget destination. Transfer stage should be able to relay at least 100MB/week of data using "store and forward"techniques.
    • The transfer stage is able toprovide any deployed SmallSat with PNT data such that its relativeposition to the transfer stage can be established autonomously aboardeither vehicle to prevent loss of spacecraft tracking, followingdeployment without direct communication with Earth assets. In additionor alternatively, if the transfer stage can be repurposedpost-deployment to provide longer term communications relay and GlobalNavigation Satellite System (GNSS)-like PNT services to thedeployed SmallSat, that is also of high interest to thesubtopic.
    • The transfer stage is able tocommunicate with any deployed SmallSat at ≥1 kbps in S-, X-, orKa-band for crosslinks of mission-critical data using Delay/DisruptionTolerant Networking (DTN) protocols, when acting as a communicationsrelay between the SmallSat and Earth.
  3. Enable small-cargo delivery andinspections to support on-orbit servicing, assembly, and manufacturingplatforms.
  4. Examine the use of lower toxicitypropellant alternatives to increase system safety for transport, groundhandling, and launch operations.

Expected TRL or TRL Range at completion of theProject: 4 to 6

Primary TechnologyTaxonomy:

  • Level 1 01Propulsion Systems
  • Level 2 01.1Chemical SpacePropulsion

DesiredDeliverables of Phase I and PhaseII:

  • Prototype
  • Hardware
  • Software
  • Analysis

DesiredDeliverables Description:

A Phase I effort should provide evidenceof the feasibility of key elements of cost, assembly, integration, andoperations through fabrication and testing demonstrations. A designconcept for flight operations, regardless of whether exploring thefull-stage concept or component/subsystem development, should reachsufficient maturity to be able to clearly define mission environmentsand performance requirements. Hardware development during the Phase Ieffort should provide confidence in the design maturity and execution ofthe Phase II effort. If the Phase I effort focuses on subsystem orcomponent development, a stage-level concept as well as a plan forsubsystem/component integration into that stage-level concept during thePhase II effort should be provided as part of the Phase I deliverable.Lastly, the Phase I effort should identify potential opportunities formission infusion and initiate partnerships or cooperative agreementsnecessary for mission execution.


The Phase II deliverableshould provide significant evidence of the progress toward missioninfusion (PMI) as outlined in the 2020 NASA Small Spacecraft Technology:State of the Art report. Phase II objectives should meet the intent ofthe In-Development or Engineering-to-Flight classifications, includingdemonstrations in a relevant environment or execution of a qualificationprogram. If the Phase I effort focused on component or subsystemdevelopment, the Phase II effort should make significant progress towardintegration into the stage-level concept design, as defined by the plansubmitted as part of the Phase I deliverable. A prototype system designshould reach sufficient maturity to define test objectives and map keyperformance parameters (mass, power, cost, etc.) from the prototype tothe flight design. Efforts leading to Phase II delivery of an integratedsystem that could be either ground tested or flight tested as part of apost-Phase II effort are of particular interest.

State of the Art and CriticalGaps:

ManyCubeSat/SmallSat propulsion units are designed for low delta-v maneuverssuch as orbit maintenance, stationkeeping, or reaction control. Largerdelta-v systems are employed for larger satellites andscience/exploration missions but are often costly and integrated as partof the satellite design. Systems typically range from cold-gas tobipropellant storables with electric systems also viable for very smallsystems. Rocket Lab has recently introduced an upgraded versionof their monopropellant kick stage, which includes a bipropellantengine, advanced attitude control, and power subsystems. Thissystem will be used for the first time for NASA's CAPSTONEmission and is suggested to have capability for orbits beyondthe lunar environment. At the component level, suppliers ofstate-of-the-art (SOA) thrusters include Aerojet Rocketdyne, Moog Inc.,and Bradford Space, among others, while companies like BlueCanyon Technologies offer spacecraft bus solutionsabsent dedicated propulsion elements. Advanced manufacturing,electric pumps and actuators, nontoxic ornontraditional propellants, and electrospray thrustersall offer potential improvements in the flightcapabilities of small propulsionsystems. System concepts that enable improved spacecraftperformance and control, such as dual-mode systems, providepotential advancements to the current SOA, especially those that enablenew science missions and those that offer potential improvements to theefficiency, accuracy, and safety of future lunar manned missions. Whilemany of these component technologies are reasonably mature, progress hasbeen limited in the development and qualification ofan integrated system as a rapid, low-cost solution fortranslunar or cislunar missions.

Deployment of small spacecraft beyondgeosynchronous orbits typically exacerbates their limitationswith respect to communications and navigation, by virtue of longercommunication distances and limited ability to use GNSS PNTservices. This typically requires the spacecraft to throttle theircommunications and rely on more cumbersome ranging transponders withEarth for position knowledge, adversely affecting spacecraft designs andoperations. Equipping transfer stages with such support servicespotentially allows for a less constraining environment for smallspacecraft deployed in deep space. With respect to the current SOA, theAir Force Research Laboratory's EAGLE mission (EvolvedExpendable Launch Vehicle (EELV) Secondary Payload Adapter (ESPA)Augmented Geostationary Laboratory Experiment), launched into a neargeosynchronous orbit, is an example of a host vehicle able todeploy smaller spacecraft as well as providing support services tohosted payload only.

Relevance / ScienceTraceability:

Thissubtopic extends the capabilities of the Flight Opportunities programand the Launch Services Program by seeding potential providers toestablish lunar/cislunar transfer capabilities. The Small SpacecraftTechnology (SST) program also seeks demonstrations of technicaldevelopments and capabilities of small spacecraft to serve as precursormissions (such as landing site investigation or in-situ resourceutilization (ISRU) prospecting) for human exploration, and ascommunications and navigation infrastructure for follow-on cislunarmissions. SST CAPSTONE is an example mission.

Many technologies appropriate for thistopic area are also relevant to NASA's lunar exploration goals.Small stages developed in this topic area would also be potential flighttestbeds for cryogenic management systems, wireless avionics, or advanceguidance systems and sensors. Sound rocket capabilities are beingimproved with options financed through this topic.

Small launch vehicles provide directaccess for a small spacecraft to the destination or orbit of interest ata time of the small-spacecraft mission’s choosing. In supportof exploration, science, and technology demonstration missions, furtherexpansion of these vehicles' reach beyond LEO is needed. Toexpand the risk-tolerant small-spacecraft approach to deep spacemissions, frequent and low-cost access to destinations of interestbeyond Earth is required. Provision of support services by the transferstage to the spacecraft post-deployment could enable more ambitioussmall-spacecraft missions.

In the longer term, technicalcapabilities of small spacecraft at Venus, Mars, or near-Earth orbit(NEO) destinations will be demonstrated by SST, and ultimately new kindsof transfer vehicles derived from these capabilities may be needed topropel them there.


  • SmallSpacecraft Technology Program.
  • SmallSpacecraft Technology Report. State of the Artof Small Spacecraft Technology | NASA.
  • LunarFlashlight Mission Overview. Whatis Lunar Flashlight? | NASA
  • CAPSTONE Mission Overview. Whatis CAPSTONE? | NASA
  • Moonbeam Mission Overview.
  • Report on Sustainable LunarInfrastructure.
  • Air Force Eagle ProgramOverview.
  • Air Force Eagle MissionArticle.
  • Example SST: Rocket Lab Photon. Satellite Solutions |Rocket Lab (
  • Example SST: Bradford Green Prop Systems. Bradford ECAPS - High Performance GreenPropulsion Thrusters
  • Example SST: AR GreenProp Systems. GreenPropulsion | Aerojet Rocketdyne
  • Example SST: ARCubesat Systems.
  • Example SST: NG ESPAStar.
  • DeepSpace Network (DSN) handbook.
  • SpaceFrequency Coordination Group (SFCG) handbook.

  • NASADelay/Disruption Tolerant Networking (DTN).

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