| Document and Entity Information | Sep. 28, 2022 |
| Entity Listings [Line Items] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Sep. 28, 2022 |
| Entity File Number | 001-39128 |
| Entity Registrant Name | Momentus Inc. |
| Entity Central Index Key | 0001781162 |
| Entity Incorporation, State or Country Code | DE |
| Entity Tax Identification Number | 84-1905538 |
| Entity Address, Address Line One | 3901 N. First Street |
| Entity Address, City or Town | San Jose |
| Entity Address, State or Province | CA |
| Entity Address, Postal Zip Code | 95134 |
| City Area Code | 650 |
| Local Phone Number | 564-7820 |
| Entity Emerging Growth Company | true |
| Entity Ex Transition Period | false |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Common Class A [Member] | |
| Entity Listings [Line Items] | |
| Title of 12(b) Security | Class A common stock |
| Trading Symbol | MNTS |
| Security Exchange Name | NASDAQ |
| Warrants [Member] | |
| Entity Listings [Line Items] | |
| Title of 12(b) Security | Warrants |
| Trading Symbol | MNTSW |
| Security Exchange Name | NASDAQ |
