TechSat-21

{{Infobox spaceflight

| name = TechSat-21

| image = TechSat21.jpg

| image_caption = Artist's rendition

| mission_type = Technology

| operator = AFRL, STP, NASA

| website =

| mission_duration =

| spacecraft_bus =

| manufacturer = MicroSat Systems

| dry_mass =

| launch_mass = {{convert|181|kg|lb}}

| power =

| launch_date = Not launched

| launch_rocket = Atlas V 401

| launch_site = Cape Canaveral SLC-41

| launch_contractor =

| orbit_epoch = Planned

| orbit_reference = Geocentric

| orbit_regime = Low Earth

| orbit_periapsis = {{convert|560|km|mi|sp=us}}

| orbit_apoapsis = {{convert|560|km|mi|sp=us}}

| orbit_inclination = 35.4& degrees

| orbit_period =

| apsis = gee

}}

TechSat-21 (Technology Satellite of the 21st Century) was a small spacecraft developed by the U.S. Air Force Research Laboratory's Space Vehicles Directorate to test technology for formation flight of spacecraft which can rapidly change formation based on mission requirements.{{cite web | url=http://www.spacedaily.com/news/radar-02b.html | title=MicroSat Systems Contract Raytheon For SAR Payload | date=2002-04-16 | accessdate=2008-07-28 | publisher=Space Daily | author=Staff Writers}} The project was canceled in 2003 due to numerous cost overruns.{{cite web | url=https://www.space.com/spacenews/archive06/formation_1204.html | title=DARPA To Solicit Bids for Formation Flying Studies | last=Singer | first=Jeremy | date=2006-12-07 | accessdate=2008-07-28 | publisher=Space News}}